Combine dry ingredients in 1-quart mixing bowl. Mix well. Add egg, buttermilk, butter and minced apple to bowl. Stir to combine (disregard any small lumps). Gently stir in blueberries. If blueberries are frozen, bake batter immediately. Otherwise, chill batter until thickened, covered airtight, at least 2 hours or overnight. Drop 2 TBS chilled batter, 2 inches apart, onto greased baking sheets. Sprinkle with more cereal, if desired. Bake in center of 425-degree oven until tops have taken slight tinge and edges are very lightly browned, about 7-8 minutes, rotating pans if browning irregularly. Do not overbake. Cool on racks. Makes 20 (3inch) muffies.