Line a 13 x 9-inch pan with aluminum foil and spray with cooking spray.
Combine corn syrup and sugar in a large microwave-safe bowl. Cook on HIGH (100%) for 2 to 2-1/2 minutes until sugar is dissolved and mixture is just starting to boil around the edges. OR cook in a large saucepan over medium heat. Add 1 cup white chocolate chips and vanilla, and stir until completely melted and mixture is smooth.
Pour over cereal in a large bowl and stir to coat completely. Pour into prepared pan; moisten hands with cold tap water and pat firmly into place.
Cool at least 30 minutes. Lift foil from pan and place on a large cutting board. Use Easter cookie cutters to cut into shapes. Spread with frosting and decorate with colored sugar as desired.
For Frosting: Beat butter, corn syrup and vanilla in a mixing bowl until light and fluffy. Gradually beat in powdered sugar and enough milk to reach desired spreading consistency.