Herbed Mushroom Spoon Bread

• 4 tablespoon unsalted butter, plus more for the pan
• 3 shallots, minced
• 1 lb button mushrooms, sliced
• 1 teaspoon fresh thyme
• Kosher salt and freshly ground pepper
• 3 cups whole milk
• 1 cup cornmeal
• 2 ounces Cheddar cheese, grated
• 4 eggs, separated

Preheat the oven to 350°F. Butter a 1 1/2-quart baking or soufflé dish.

In a sauté pan, melt 2 tablespoons of the butter over medium heat. Add the shallots and cook until softened, stirring occasionally, about 3 minutes. Add the mushrooms and thyme, season with salt and pepper, and cook, stirring occasionally, until the mushrooms are cooked and any liquid has evaporated, about 8 minutes. Remove from the heat.

In a heavy-bottomed saucepan, heat the milk over medium-high heat until bubbles form around the edges. Slowly whisk in the cornmeal, reduce the heat to low, and cook, whisking constantly, until the mixture thickens, about 10 minutes. Remove from the heat and stir in the remaining 2 tablespoons butter and the Cheddar cheese. Add the egg yolks, one at a time, whisking to combine after each addition.

In a medium bowl, whip the egg whites until medium-stiff peaks form—the tips of the peaks curl down slightly when the beaters are lifted. Gently fold the whipped egg whites into the batter. Pour the mixture into the prepared baking dish.

Bake until the spoon bread is puffed and golden brown, about 50 minutes. Serve immediately.