Place one layer of potatoes in bottom of 9 x 13 inch casserole dish. Pour melted butter combined with garlic powder over potatoes. Mix together cheeses and flour. Sprinkle 1/3 of cheese mixture over potatotes. Repeat two more layers of potatoes and cheese. Then pour 1/2 and 1/2 over mixture. Bake at 375 degrees for 1 hour.