Cheese, Onion and Bread Souffle

This recipe is from Real Simple. It's not! But it's a fun use for old bread - savory, fluffly, hot, delicious!

Ingredients:
2 Tbs. butter, plus more for the dish
10 slices (about 10 ounces) stale soft white or sourdough bread, crusts removed and torn into ½-inch pieces
2 cups hot milk
1 small onion, sliced
4 eggs, separated
7 ounces Swiss cheese, grated
1 tsp. kosher salt
1/4 tsp. freshly ground black pepper
1 pinch ground nutmeg
1 pinch ground cayenne pepper

Preheat oven to 400° F. Butter a 2 - 2 ½ quart soufflé dish; set aside. Place bread in a shallow bowl and pour the milk over it. Set aside until the liquid is absorbed.

Melt the 2 Tbs. of butter in a medium skillet over medium-low heat. Add the onion and sauté until tender, about 15 minutes. Remove from heat. Mash the bread with your hands or a spoon and stir in the onions. In a medium bowl, whisk together the egg yolks, cheese, salt, pepper, nutmeg, and cayenne. Pour the mixture over the bread, stirring until well combined. In a separate bowl, beat the egg whites until stiff peaks form, then gently fold them into the bread mixture in 3 additions. Transfer to the soufflé dish and bake until golden and firm, 45-50 min.