Pour water over 100% Bran and let stand. In very large bowl, cream butter, sugar and eggs. Add buttermilk and then bran mixture. Stir until blended. Stir flour, soda, salt and add to above mixture; mix well. Add bran flakes and fold in until just moist. Add raisins or dates. Chill 1 day before baking. Bake at 350° for 15 to 20 minutes. Batter may be kept in refrigerator for up to 6 weeks. Makes 6 dozen muffins