If you love rhubarb and date bars/matrimonial squares you'll LOVE these Rhubarb Squares. These Rhubarb Squares, also known as Rhubarb Crumble Bars, have a delicious rhubarb compote filling that's the perfect balance between sweet and tart, nestled between a scrumptious oatmeal base and topping. They are ideal for using up an abundance of rhubarb to make a perfect spring dessert or snack!
Although I freeze fresh rhubarb and use it all year round, I can never seem to get enough and can't wait for it to come up in the spring. These Rhubarb Oatmeal bars were inspired by my date squares, which also make a great dessert after a lovely spring meal. Try it with my Spring Salad with Fiddleheads & Blackberry Vinaigrette. This is the best rhubarb dessert!
🍒Reader Review
"Hi, Terry. I just made this recipe. (July 7, 2024) It's a keeper. Just the way I'd want an oatmeal rhubarb square to taste.!" ⭐⭐⭐⭐⭐
And even if you're not a rhubarb lover, you won't be able to get enough of these squares- they are totally addictive. Spring is here and that means rhubarb reason!
l only started growing my own rhubarb a couple of years ago so I get really excited when it starts to come in! Be sure to check out my other rhubarb recipes! If you love oats and rhubarb, you're sure to love my Old Fashioned Rhubarb Crumble too!
Looking for a rhubarb recipe that's a bit lighter/lower calorie? Be sure to try my Healthy Rhubarb Bread or my Healthy Rhubarb Muffins!
🥘Ingredient Notes
For this rhubarb oatmeal bar recipe, you'll need:
- Quick rolled oats. I use quick rolled oats or "quick oats" because they cook faster than regular rolled oats. Do NOT use instant oats - they will turn to mush!
- Butter. I use unsalted butter, as I like to control the salt in my butter.
- Rhubarb. You can use fresh or frozen rhubarb, but make sure you defrost and drain frozen rhubarb and measure after you have done that.
- Cornstarch. Cornstarch thickens the filling without affecting the flavor.
- Red food coloring (optional) (affiliate link) Add a little food coloring to your rhubarb compote so it looks more appetizing (red and not brown). I like to use Americolor super red (affiliate link) so I use less food coloring.
*See recipe card for full list of ingredients and quantities
📖Variations & Substitutions
- Lemon zest - you can use 2 teaspoons of lemon juice instead or use orange zest
- Rolled Oats- if you only have old-fashioned/regular rolled oats you can put them in your food processor and pulse them a couple of times to break them down and use them as a substitute for quick rolled oats.
- Sugar - some readers find this too sweet. You can start with less sugar in the filling, and add more at the end to your desired sweetness. Neither I nor my family likes things overly sweet and we found this perfect!
🔪Step-by-Step: How to make Rhubarb Squares
- Step 1: Filling: Cut rhubarb into ½-inch pieces. In a medium saucepan, combine rhubarb with 1 ½ cup sugar and lemon zest, on the stovetop on medium heat. Cook until tender, (about 15 minutes).
- Step 2: Combine ½ cup sugar and with cornstarch, stir into cooked rhubarb.
- Step 3: Continue cooking for an additional 10 minutes (approximately) until rhubarb is completely broken down (as shown). Cool.
- Step 4: To achieve a pink color, add food coloring, if desired.
- Step 5: Base & Topping: Preheat oven to 375 degrees F/ 190 degrees C. Spray a 9X13 pan with non-stick cooking spray. In a medium bowl, stir flour, baking soda, brown sugar, cinnamon, and oats together. Cut in cold butter into dry ingredients using a pastry cutter (or see my top tip below for an easier way to cut in butter).
- Step 6: Assembly: Pat ½ the mixture into prepared baking pan.
- Step 7:Then add rhubarb mixture on the bottom crust. Spread evenly with a rubber spatula.
- Step 8: Add the remaining flour/oat crumb topping mixture over the rhubarb layer.
- Step 9: Bake in preheated oven for 35 - 40 minutes or until lightly browned on top. Cool and cut into squares. Garnish with whipped cream and cinnamon sprinkles, if desired.
Hint: It's important to wait until rhubarb squares are completely cooled before cutting, otherwise they will fall apart. You can put them in the freezer to speed up the process!
Expert Recipe Tips
- Use a glass pan or coated pan for best results. Rhubarb is acidic - you shouldn't cook rhubarb in aluminum, copper, or iron pans that react. In metal pans, rhubarb turns brownish and the pan discolors.
- Use Quick Oats for the Best Texture. Quick oats provide the perfect balance between chewiness and crunch. If using old-fashioned rolled oats, pulse them in a food processor a few times to break them down. Avoid instant oats, as they can become mushy.
- Freeze the Butter for Easy Mixing. For the best crumb texture, keep your butter very cold. Grating frozen butter into the dry ingredients makes it easier to incorporate evenly without overmixing.
- Don't Skip the Cornstarch. Cornstarch thickens the rhubarb filling, preventing it from being too runny. Without it, your squares might turn out too soft and messy.
- Let the Bars Cool Completely Before Cutting. If you cut them while they're still warm, they will likely fall apart. Speed up the cooling process by placing them in the fridge or freezer.
- Adjust the Sweetness Based on Your Rhubarb. Rhubarb can vary in tartness. Taste your cooked filling before assembling and add a little more sugar if needed.
- Optional: Enhance the Color Naturally. If you prefer to skip food coloring, adding a handful of chopped strawberries to the rhubarb filling can give it a more vibrant red hue.
- Make It Ahead. These bars store well! You can bake them a day ahead and refrigerate them overnight for the best texture.
🌡️Storage
Store these rhubarb oatmeal bars in the fridge in an airtight container for up to 4 days (if they last that long!) and freeze them for up to 3 months in a sealed container.
👪 Serving Size
This rhubarb bars recipe makes 16 square servings. However, you can cut them in half (into triangles) and get 32 servings.
You can also half, double, or triple the recipe by clicking on the serving number and selecting the number of servings you'd like. The ingredient quantities will automatically adjust. If you half the recipe, you'll need a 9-inch pan (square) and if you double it, you'll need an additional 9X13 pan.
Top tip
Keep your butter frozen (or at least very cold) and grate it into the recipe. It's easier and less messy!
❔ Recipe FAQs
To freeze rhubarb, cut off the bottom of the rhubarb stalks, wash and chop stalks into approximately ½ inch pieces. Add 3-4 cups to a large Ziplock freezer bag. Before you use it in a recipe, thaw it completely, drain off excess water, and measure it at that point.
Do you have to peel rhubarb before you cook it?
There is no need to peel rhubarb before you cook it. Rhubarb will break down when cooked, so it's no longer stringy.
You can slightly reduce the sugar in the filling, but keep in mind that rhubarb is quite tart, so cutting too much sugar may result in a sour taste. If you want to use a sugar substitute, I recommend using Monk fruit, but you'll only need to use half the amount.
Yes! Substitute the all-purpose flour with a gluten-free flour blend and ensure your oats are certified gluten-free.
If you are looking for a rhubarb square recipe or simply a way to use up your rhubarb harvest, you'll love this one!
And be sure to try my No Bake Rhubarb Cream Cheese Bars!
More Rhubarb Recipes
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📋 Rhubarb Square Recipe
Equipment
Ingredients
Filling
- 4 cups rhubarb
- 2 teaspoon lemon zest
- 2 cups sugar
- 2 ¾ tablespoon cornstarch
- Drop red food colouring optional
Base & Topping
- 1 ½ cups all-purpose flour
- 1 cup brown sugar
- 1 ¾ cups rolled oats
- 1 cup cold unsalted butter
- ¼ teaspoon baking soda
- ½ teaspoon cinnamon
Instructions
Filling
- Cut rhubarb into ½ inch pieces. In a medium saucepan, cook rhubarb with 1 ½ cup sugar and lemon zest, on stovetop on medium heat, until tender, (about 15 minutes).4 cups rhubarb, 2 tsp lemon zest, 2 cups sugar
- Combine ½ cup sugar and with cornstarch, stir into cooked rhubarb.2 ¾ tbsp cornstarch
- Continue cooking for about 5-10 additional minutes, until rhubarb has broken down. Cool
- To achieve a pink color, add food colouring, if desiredDrop red food colouring
- Preheat oven to 375 degrees F/190 degrees C. Spray a 9X13 pan with non-stick cooking spray.
Base
- In a large mixing bowl, stir flour, baking soda, brown sugar, cinnamon, and oats together. Cut in cold butter.1 ½ cups all-purpose flour, 1 cup brown sugar, 1 ¾ cups rolled oats, 1 cup cold unsalted butter, ¼ tsp baking soda, ½ tsp cinnamon
- Pat ½ the mixture into the bottom of the pan.
- Then add rhubarb filling mixture on top. Spread evenly with a rubber spatula.
- Add remaining flour/oat crumb topping mixture over rhubarb layer.
- Bake in preheated oven for 35 - 45 minutes or unti lightly browned.
- Cool and cut into squares. Serve with a dollop of whipped cream and a sprinkle of cinnamon, if desired. Hint: It's important to wait until rhubarb squares are completely cooled before cutting, otherwise they will fall apart. You can put them in the freezer to speed up the process!
Notes
-
- Use a glass pan or coated pan for best results. Rhubarb is acidic - you shouldn't cook rhubarb in aluminum, copper, or iron pans that react. In metal pans, rhubarb turns brownish and the pan discolors.
-
- Use Quick Oats for the Best Texture. Quick oats provide the perfect balance between chewiness and crunch. If using old-fashioned rolled oats, pulse them in a food processor a few times to break them down. Avoid instant oats, as they can become mushy.
-
- Freeze the Butter for Easy Mixing. For the best crumb texture, keep your butter very cold. Grating frozen butter into the dry ingredients makes it easier to incorporate evenly without overmixing.
-
- Don't Skip the Cornstarch. Cornstarch thickens the rhubarb filling, preventing it from being too runny. Without it, your squares might turn out too soft and messy.
-
- Let the Bars Cool Completely Before Cutting. If you cut them while they're still warm, they will likely fall apart. Speed up the cooling process by placing them in the fridge or freezer.
-
- Adjust the Sweetness Based on Your Rhubarb. Rhubarb can vary in tartness. Taste your cooked filling before assembling and add a little more sugar if needed.
-
- Optional: Enhance the Color Naturally. If you prefer to skip food coloring, adding a handful of chopped strawberries to the rhubarb filling can give it a more vibrant red hue.
-
- Make It Ahead. These bars store well! You can bake them a day ahead and refrigerate them overnight for the best texture.
- Lemon zest - you can use 2 teaspoons of lemon juice instead or use orange zest
- Rolled Oats- if you only have old-fashioned/regular rolled oats you can put them in your food processor and pulse them a couple of times to break them down and use them as a substitute for quick rolled oats.
- Sugar - some readers find this too sweet. You can start with less sugar in the filling, and add more at the end to your desired sweetness. Neither I nor my family likes things overly sweet and we found this perfect!
Claire M says
I made this with frozen rhubarb and it was excellent. Sometimes frozen rhubarb can be challenging because it makes things too wet (like crumble or pie). With this recipe, due to the long cooking and the cornstarch, you can be sure the filling isn't too wet even when made with frozen fruit.
I also made the same recipe with plums from this year's plum harvest, cooking down about 4 cups of chopped plums in a similar way to the rhubarb. The plums took a bit longer cooking time. It was just as tasty made with plums and was a wonderful way to use them (other than my usual plum jam). I think the recipe would adapt to almost any kind of fruit that is cooked down into a thick, jam-consistency kind of filling. I've added this to my favourite recipe list!
Terri Gilson says
Hi Claire,
I'm so glad to hear you loved the recipe and were even able to make it with another fruit. Thanks for sharing!
Terri
DeeDee Mow says
HOLY BUTTER BATMAN !! I had to keep adding more flour , then oats , then brown sugar lt was a big lump of butter not crust or topping . I don't know how anyone could even get it into the baking dish ! So with my additions we will see how it turns out
Terri Gilson says
Hi DeeDee,
I’m sorry to hear you had such a frustrating experience in the kitchen!
This is one of my most popular recipes and has been a staple for many readers for years without this issue. When a shortbread-style crust or topping turns into a 'lump of butter' rather than a sandy crumble, it usually points to a couple of specific kitchen variables:
Butter Temperature: For a perfectly crumbly texture, the butter must be ice-cold when mixing. If the butter is too soft or partially melted, it will bind too quickly with the flour and turn into a greasy dough rather than a light crumble.
Measurement: It is important to double-check the butter-to-flour ratio. If the butter is measured correctly and kept cold, it should easily incorporate into the dry ingredients to create that spectacular, crisp texture everyone raves about.
I hope your additions helped save the batch and that they still turned out tasty! If you decide to try them again, I recommend using butter straight from the fridge (or even the freezer) for the best results.
Sincerely,
Terri
Connie says
I accidentally bought a bag of frozen rhubarb instead of strawberries, and I found this recipe. I followed as it was written, I did add in some strawberries. I think this is the first thing I’ve ever made with rhubarb! It was delicious! And got better the second and third day - my husband really liked them also.
Terri Gilson says
Hi Connie,
So glad to hear you loved your first rhubarb recipe, as did your husband! I have lots more you might like!
Thanks,
Terri