Preheat oven to 400 degrees. Grease or paper line 12 muffin cups. Combine cereal, buttermilk, egg and oil in bowl. Let stand 5 minutes, stir to break up cereal. Combine flour, sugar, baking powder and cinnamon in separate bowl. Add cereal mixture all at once to flour mixture, stirring just until combined. Divide evenly among prepared muffin cups. Sprinkle with topping. Bake 20 to 25 minutes or until tester inserted in center comes out clean.
To prepare topping: Combine cereal, sugar and butter; mix well. Divide evenly over muffins.