Prepare fiddleheads: Rinse the fiddleheads, remove any papery brown skin from the tops, and then slice off as much of the brown parts on their ends as you can. Fill a large bowl with cold water and put the fiddleheads in there for a few minutes, swishing them around with your hands to remove any dirt. * I rub the coils to loosen any dirt as well. Discard the water and repeat this process. Add to pot of cold water and bring to a boil. Boil for 15 minutes (time it from the time the water is a full boil) Drain. * They will be a little darker green in color. *Set a few aside for garnish at this point
Melt butter in a large pot, over medium-high heat. Stir in onion and garlic; cook and stir until onion has softened and turned translucent, about 5 minutes.
Pour 4 cups chicken broth, grated carrots, and fiddleheads into the onion mixture, and bring to a full boil.
Reduce heat to medium-low, uncovered and simmer until vegetables are tender, about 15 minutes.
Remove vegetables with a slotted spoon and place in food processor.
Puree in a food processor or use an immersion blender and puree right in the pot.
Then return puree mixture to soup, whisking to combine.
Remove from heat and whisk in Greek yogurt, milk and cheese.
Add fresh dill, Worcestershire sauce, and soy sauce. cook on low and stirring with a whisk, until heated through, about 5 minutes.
Add salt and pepper to taste.
At this point, if the soup is not thick enough for your liking, add a roux (mix equal amounts of flour and oil - about 1.5 tbsps of each) and whisk into soup. Keep whisking over low heat until soup reaches the desired thickness. Repeat until desired thickness is reached.
Garnish with Cheddar cheese additional fiddleheads or fresh dill