Scalloped Potatoes

Preheat oven to 400°F. Spray a 9x13-inch baking dish with cooking spray.

Melt butter in a large pan over medium heat. Add onion and saute for 5-6 minutes, until they begin to soften and turn translucent. Add garlic and saute another 1-2 minutes.

Sprinkle onions, butter, and garlic with flour and stir until evenly dispersed, continuing to cook for 1 minute.

Slowly whisk in the milk and cream until combined so there are no lumps of flour. Add salt and pepper, to taste. Continue to cook for another 1-2 minutes, just until the sauce begins to thicken and barely starts to simmer around the edges of the pan. Do not let it come to a boil. Remove from heat and set aside.

Spread half of the sliced potatoes in the bottom of the prepared casserole dish in an even layer. Top with half the sauce and onions. Sprinkle with half of the cheddar cheese and all of the Parmesan cheese. Top with another layer of the remaining potatoes, remaining sauce and onions, and remaining cheese.

Cover with foil and bake for 45 minutes. Remove foil and bake uncovered an additional 30-45 minutes, until browned on top and potatoes are cooked through. If the cheese on top begins to brown too much, recover with foil to finish baking.