Ingredients
9 tablespoons unsalted butter
1 one-pound bag frozen pearl onions, thawed and drained
3 pounds assorted mushrooms, such as button, cremini, or shiitake, trimmed and cut in half (large ones should be quartered)
3/4 cup heavy cream
1 cup freshly grated Parmesan cheese (4 ounces)
1 teaspoon coarse salt
1/4 teaspoon freshly ground pepper
1 cup plain coarse breadcrumbs, preferably homemade
Preparation
Preheat oven to 350 degrees. Heat 1 tablespoon butter in a large cast-iron or ovenproof skillet over medium-high heat. Add onions, and cook until soft and just starting to brown, about 5 minutes. Transfer to a large mixing bowl.
Working in four batches, melt 2 tablespoons butter in same skillet; add one-quarter of the mushrooms, tossing to coat evenly with butter. Cook until mushrooms have released their juices and most of the juices have evaporated, about 5 minutes. Transfer to bowl with onions. Repeat process with remaining butter and mushrooms.
Add heavy cream, 1/2 cup Parmesan, salt, and pepper to bowl; stir until combined. Return the mixture to skillet or transfer to a large baking dish. Sprinkle breadcrumbs and remaining 1/2 cup Parmesan over the top.
Bake until bubbling and nicely golden on top, about 25 minutes. Remove from oven. Serve hot.
