Preheat the oven to 400 Degrees F. Butter a 2-qt casserole and set aside. Melt the 3 tb of butter in a 2-quart saucepan, on moderate heat, and add the flour; cooking for 2 minutes, stirring constantly. Add the milk and cook until thickened, stirring constantly. Add the cheddar cheese and stir until melted. Remove from the heat and stir in the ham and onion flakes. Stir in 1 cup of potato slices. Pour into the prepared casserole. Arrange the remaining potato slices on the top of the Ham mixture. Melt the remaining butter and brush on the potato slices. Sprinkle with the minced parsley and bake for 20 minutes or until heated through. Serve hot.