Kinda winged this one tonight, but it turned out great.  Slice 5 russet potatoes thin and half an onion, layer in square baking dish. In saucepan, make a roux ( melt 2Tbsp. butter, add 2Tbsp. flour, wisk in 2 cups 2% milk, salt, pepper) cook til sauce thickens.  Remove from heat, add 1cup shredded cheddar cheese, 1cup extra sharp cheese (use any cheese you like) and pour over potato and onions. Add salt and pepper to taste, parsley flakes and sprinkle italian breadcrumbs on top.  Bake, covered at 350 for 1-1 1/2 hours. Makes approx. 6-8 servings.