Crab Risotto with Oyster Mushrooms

Name: Crab Risotto with Oyster Mushrooms
Ingredients: 3/4 pound oyster mushrooms, cut into 1 1/2-inch pieces; 1/4 cup plus 2 tablespoons extra-virgin olive oil; Kosher salt; Freshly ground pepper; 4 tablespoons unsalted butter, cubed; 3 cups fish stock or bottled clam juice; 1/2 medium onion, minced; 1 1/2 cups arborio rice; 1/4 cup dry white wine; 2 tablespoons freshly grated Parmigiano-Reggiano cheese, plus more for serving; 1 pound Dungeness or other lump crabmeat, picked over for shells; 1/4 cup finely chopped chervil or parsley, for garnish