Cook enough sweet potatoes (6 to 8 medium sized) for 1 13 x 9 x 2 Pryex pan. Can cook day before or several hours before. Cool, peel and cut in half or slice. Melt 1 cube of butter. Stir in 1 package brown sugar. Spoon on to sliced sweet potatoes. Bake at 350 degrees for 1 hour. Can add large marshmallows to top if you wish before serving.