Coat 13 x 9 x 2-inch microwave-safe dish with cooking spray. Arrange graham crackers in single layer in dish, breaking crackers as needed to fit. Sprinkle marshmallows evenly over crackers.
Microwave on HIGH 1.5 minutes or until marshmallows are puffy. Remove from microwave. Stick pan in the freezer to cool.
In 2-quart microwave-safe mixing bowl combine chocolate morsels, corn syrup and butter. Microwave on HIGH about 1 1/2 minutes or until chocolate is melted, stirring every 30 seconds. Stir in peanut butter. Add krispies cereal, mixing until combined.
Spread evenly over marshmallows. Shake sprinkles on top, for fun! Cover and refrigerate about 1 hour or until firm. Cut and store in airtight container in refrigerator.