Step 1

Place 1 ounce dried porcini mushrooms in a medium heatproof bowl and cover with 1 1/2 cups boiling water. Soak until mostly softened, about 15 minutes. Meanwhile, dice 1 medium yellow onion and mince 2 garlic cloves. Melt 4 tablespoons unsalted butter in a Dutch oven or heavy-bottomed pot over medium heat. Add the onion, garlic, and 1 pound sliced cremini mushrooms, and season with 1 1/2 teaspoons kosher salt and 1/4 teaspoon black pepper. Cook, stirring occasionally until the mushrooms are softened and have released their juices, 10 to 12 minutes.

Step 2

Line a fine-mesh strainer with cheesecloth. Pour the soaked mushrooms through the strainer into a measuring cup or bowl. Reserve the liquid and coarsely chop the mushrooms (leave behind any grit trapped in the cheesecloth).

Step 3

Sprinkle 3 tablespoons all-purpose flour into the pot and stir to coat the vegetables. Cook until lightly browned, stirring regularly, about 2 minutes. Pour in 4 cups low-sodium vegetable or chicken broth and scrape the bottom of the pot with a wooden spoon. Stir in the reserved soaking liquid from the mushrooms, the chopped porcini mushrooms, 2 tablespoons soy sauce, 2 teaspoons dried thyme, and 2 bay leaves. Bring to a boil. Reduce the heat to low and simmer uncovered until the flavor is developed and the soup is slightly thickened, about 30 minutes.

Step 4

Remove and discard the bay leaves. Transfer about 2 cups of the soup to a blender or food processor and purée until smooth. Stir the purée back into the pot. Remove from the heat and stir in 1/2 cup heavy cream.