In large mixing bowl beat peanut butter and butter on medium speed until combined. Add powdered sugar and milk. Beat until fluffy. Stir in KELLOGG'S® RICE KRISPIES® cereal, mixing until thoroughly combined. Press mixture evenly into 8 x 8 x 2-inch pan coated with cooking spray. Refrigerate until firm.
Drizzle chocolate over cereal mixture. Refrigerate about 30 minutes or until chocolate is set and cereal mixture is firm. Cut into bars. Store in airtight container in refrigerator.