1. Heat oven to 375°F. Remove wrappers from peanut butter cups.
2. Beat butter, peanut butter, brown sugar and granulated sugar in large bowl until light and fluffy; blend in egg. Stir together flour and baking soda; add to butter mixture. Shape dough into 1-inch balls. Stir together egg white and water; beat with fork until foamy. Roll balls in egg white mixture, then in crushed cereal. Place on ungreased cookie sheet; press with thumb or finger tips in center making an indentation.
3. Bake 8 to 10 minutes or until cookies are set. Remove from oven; immediately press peanut butter cup onto each cookie. Cool 1 minute; remove carefully from cookie sheet to wire rack. Cool completely. Makes about 42 cookies.