Microwave chocolate, corn syrup and butter in large microwaveable bowl on high 2-1/2 min. or until butter is melted, stirring after 1-1/2 min. Stir until chocolate is completely melted and mixture is well blended. Stir in vanilla.
Add cereal; mix well. Press firmly into greased 9-inch square pan.
Refrigerate 15 min. or until set. Cut into 12 bars to serve. Makes 1 dozen.