Drain the sliced pineapple. Mix crushed corn flakes and 3 tablespoons brown sugar in a shallow dish and set aside. Spray a cookie sheet with PamŽ. Place 10 slices of pineapple on cookie sheet. Drain sweet potatoes. Mash them with a fork. Add 1 cup brown sugar, lemon extract, cinnamon, nutmeg and margarine. Beat with an electric mixer until fairly smooth. With your hands, form 10 balls of the sweet potato mixture and roll in corn flakes mixture, coating well. Place a ball on each pineapple slice and top with a cherry. Refrigerate until ready to bake. Dot with extra butter and bake at 350 degrees F for 25 minutes.