Beat butter and sugar with electric mixer on medium speed until creamy.
Add egg yolk; beat until well blended.
Add flour; mix well. Stir in 1 cup of the cereal.
Roll level tablespoonfuls of dough into balls; place on ungreased baking sheets. Flatten each ball, then make 3 indents on one side of each for "pawprint."
Bake at 350F for 12 minutes of until lightly browned. DO NOT OVERBAKE.