Giovanna's Yummy Cheese Onions

Preheat the oven to 400 degrees F (200 degrees C).

Melt 1/4 cup of butter in a large skillet over medium-low heat. Add sliced onions, and cook until wilted and soft, but not browned. Set aside.

Melt the remaining butter in a saucepan over medium heat. Mix in the flour, salt, pepper, and dry mustard. Cook stirring for 2 minutes. Gradually whisk in milk, stirring constantly until thickened. Add cheese, and cook, stirring until melted. Set aside.

Spread half of the onions into the bottom of a 1 quart casserole dish or 11x7 baking dish. Spoon half of the sauce over the onions, then sprinkle with half of the bread crumbs. Repeat layering, and spray the top layer of bread crumbs with cooking spray.

Bake uncovered for 25 minutes in the preheated oven, then turn on the broiler, and broil for 1 minute, until the top is golden brown.