Line muffin tin with paper bake cups and set aside. Preheat oven to 400F. In a medium mixing bowl combine flour, cornmeal, granulated sugar, baking powder, and salt. Make a well in the center of the dry ingredients. In a small mixing bowl combine egg, buttermilk, vegetable oil, and lemon peel. Add egg mixture all at once to dry ingredients. Stir just until moistened - batter should be lumpy. In a small mixing bowl, combine Craisins® and walnuts (optional) and fold into muffin batter. Spoon batter into muffin tin, filling each 2/3 full. Top each muffin with some of the reserved sugar. Bake for about 20 minutes or until golden. Remove muffins from muffin cups. Cool slightly on a wire rack. Griddle prior to serving: heat skillet with pat of butter. Split a muffin in half lengthwise. Once butter is bubbling, place muffin split-side down and heat until evenly golden.