Preparation - Spray a 2 quart casserole with non-stick cooking spray; set aside. In a large skillet, over medium heat, saute onions in butter until they become transparent. Crush saltines in a blender or food processor. Reserve 3 T. saltine crumbs for topping. Place remaining saltine crumbs in the bottom of casserole, Remove onions from skillet with a slotted spoon. Place soup & onions in casserole alternating layers until full. Combine milk and eggs; pour over onions. Top with grated chedder cheese and remaining saltine crumbs. Bake at 350° for 25 to 30 minutes or until lightly browned and bubbly.
