Apple, Onion and Gruyere Gratin

Have mimosas with this warming, winter brunch : ) This meal is a tribute to Maureen and Daniel, who continue to encourage me to cook with butter, and to my mom, who shared this brunch with me on Thanksgiving morning.

Ingredients:
2 apples, sliced into quarters, and then into thirds
1 large onion or 2 medium onions, sliced into moon-shaped crescents (but not too thinly)
1 tablespoon of flour
1 tablespoon of butter
1 cup of milk
1 teaspoon of nutmeg
1/2 teaspoon salt
dusting of breadcrumbs, about 1/4 cup
walnuts to taste

Begin by sauteeing onions with nutmeg and BUTTER! until the onions are half-way cooked. Set aside. Slice the apples directly into a 9 X 9 baker's dish and add the onion mixture. Mix the two together, so the apples get coated in the nutmeg-onion mixture. In a small saucier, begin your roux. Melt and brown the butter for a few moments before adding your flour. With a wisk, let the flour-butter mixture cook. When bubbly, add the cup of milk. Raise the heat to gently scald the roux without burning, and continue to wisk until the mixture thickens. At that point, lower the heat, and let the mixture summer. Now you have all the ingredients to begin layering your baking dish. Add the cheese over the apple-onion mixture, then the sauce, then the breadcrumbs and walnuts. Bake at 350 degrees for about 30 minutes. Enjoy!