1 large yellow onion, thinly sliced Pinch of sugar
Kosher salt and freshly ground black pepper
2 tablespoons all purpose flour
2 teaspoons chopped fresh thyme
3 cups coarsely chopped fiddleheads (washed and trimmed)
4 cups low sodium chicken broth
½ cup fresh Italian parsley leaves
¾ cup sour cream Milk, for thinning the sour cream
In a large saucepan, melt the butter in the olive oil over medium heat. When the butter is melted, add the onions and season with the sugar, salt and pepper. Cook, stirring frequently, until the onions are a deep golden color, about 15 minutes. You may have to adjust the heat while you cook so the onions don’t burn. With tongs, remove half of the onions to a small bowl and reserve.
Add the flour and thyme to the saucepan and cook, stirring, for a minute. Add the fiddleheads and the stock. Bring to a simmer and cook until the fiddleheads are very tender, about 10 to 15 minutes. Season with salt and pepper.
Puree the soup with 1/2 cup of the sour cream in batches in a blender (or with a hand held immersion blender right in the pot). Thin the remaining ¼ cup sour cream with 1 to 2 tablespoons milk, to the consistency of heavy cream.
To serve, ladle the soup into warmed soup bowls. Drizzle each serving with some of the sour cream and swirl in some of the reserved caramelized onions.