Those oversized, dark, densely textured mushrooms you see sitting alongside the more delicate button mushrooms in the produce department are portobellos. They are delicious sliced and sautéed or grilled like a burger, and are perfect for a cold weather soup. Portobello mushrooms are rich and meaty which makes this soup aromatic and intensely flavored without the addition of a long list of ingredients. This is a perfect start to a Thanksgiving meal
4 tablespoons unsalted butter
2 leeks white and light green parts only, halved lengthwise, and thinly sliced
1 large (about 12 ounces) yellow onion chopped
3 large (about 1 pound) portobello mushrooms wiped or brushed clean, and chopped
3 tablespoons all-purpose flour
6 cups homemade chicken stock or canned low-sodium chicken broth
1½ tablespoons fresh thyme leaves
1 bay leaf
1 teaspoon salt
1 teaspoon sugar
½ teaspoon freshly ground pepper
1 cup heavy (whipping) cream
Parmesan-and-Herb Croutons (recipe follows)
5 cups fresh bread cubes (3/4-inch cubes), cut from a loaf of artisan bread, crusts removed
1/4 cup extra-virgin olive oil
1/2 cup (2 ounces) Parmesan cheese, freshly grated
1/4 teaspoon freshly ground pepper
1 tablespoon minced fresh thyme leaves
1/2 tablespoon minced fresh oregano
In a 6- to 8-quart saucepan, melt the butter over medium heat. Swirl to coat the bottom of the pan and sauté the leeks and onions, stirring constantly, until slightly softened and well coated with butter, about 2 minutes. Reduce the heat to very low, cover the pan, and cook for 30 minutes, stirring occasionally. Add the mushrooms, stir to combine, cover, and cook 10 minutes longer. Raise the heat to medium, stir in the flour and cook 3 minutes. Add the chicken broth, thyme, bay leaf, salt, sugar, and pepper. Simmer, partially covered, 10 minutes longer.
Cool the soup for about 10 minutes; discard the bay leaf, and then purée the soup in batches in a blender or food processor fitted with the metal blade. (Alternatively, use an immersion blender and puree the soup right in the pan.) Return the puréed soup to the saucepan and add the cream. Cook over low heat until heated through, but do not let the soup boil. Taste and adjust the seasoning. Ladle the soup into a warmed soup tureen or individual bowls, garnish with the croutons, and serve immediately.
To make the croutons, preheat the oven to 375°F. In a large bowl, combine the bread cubes with the olive oil, Parmesan, and pepper and toss to coat evenly. Transfer to a rimmed baking sheet and bake for 6 minutes. Sprinkle the herbs over the bread cubes, toss to combine, and continue to bake until the bread cubes are crisp and golden, about 6 minutes longer.
The croutons can be made up to 2 days in advance. Store in a lock-top plastic bag or airtight container at room temperature.
The soup can be made up to 3 days ahead. Let cool and refrigerate in a covered container. Rewarm gently just before serving, and garnish with the croutons.