PREHEAT oven to 375°F. Beat butter, sugars, peanut butter and egg until creamy. Mix flour, baking powder, baking soda and salt in large bowl. Stir in cereal. Add alternately with milk to peanut butter mixture, beating until well blended after each addition.

SPOON evenly into 12 paper-lined muffin cups, filling each cup three-quarters full.

BAKE 20 min. or until wooden toothpick inserted in centres comes out clean. Cool in pan 5 min.; remove to wire racks. Serve warm or cooled.