8 squares (225 g pkg.) semi-sweet chocolate, coarsely chopped
Lightly grease 13×9-inch baking pan; line with parchment paper, 2 ends extending over edge of pan.
Set aside 60 (approx. 3/4 cup) whole Shreddies for topping. Place remaining Shreddies in a resealable plastic bag and crush by hand to yield 1-1/2 cups coarse crumbs.
Microwave peanut butter and butter in large microwaveable bowl on HIGH 45 sec., or until butter has melted; stir to combine. Stir in sugar and crumbs.
Spread mixture into prepared pan, patting down to form a firm crust.
Microwave chocolate in medium microwaveable bowl on MEDIUM 2-3 min., stirring once. There should still be some unmelted chunks. Stir until all chocolate is melted and smooth.
Spread evenly over crust. Arrange 60 Shreddies over top, forming rows of 6 x 10.
Cool at room temperature 20 min. Using sharp paring knife, score chocolate along rows, to form 60 squares. Refrigerate 1 hour. Using parchment paper ends, carefully lift mixture from pan and place on cutting board. Cut into 60 squares.