Line a 15x10x1-inch banking pan with foil; extend over the edges of pan; set aside.
In a large saucepan, combine granulated sugar and corn syrup.
Heat and stir just until mixture bubbles around edges.
Heat and stir for 1 minute more.
Remove from heat.
Stir in peanut butter until melted.
Stir in rice cereal and cornflakes until coated.
Press mixture into the bottom of the prepared pan.
For pudding layer, in a medium saucepan melt ¾ cup of the butter.
Stir in powdered sugar, dry pudding mixes, and the milk.
Spread pudding mixture over cereal layer; set aside.
For frosting, in a small saucepan heat and stir chocolate pieces and the remaining ½ cup butter over low heat until smooth; spread over pudding layer.
Cover, chill 1 hour or until set.
Lift form pan and cut into bars.
