In a large mixer bowl beat margarine or butter till softened; beat in 1.5 cups powdered sugar and vanilla. Add flour, cocoa powder, cornstarch, and salt; beat till smooth. Stir in chopped peanuts. Reserve 1.3333333333333 cups of cocoa mixture. Spread remaining cocoa mixture in the bottom and up the sides of an ungreased 25 cm tart pan with a removeable bottom, or in the bottom and 3 cm up the sides of a 25 cm springform pan. In a bowl stir together peanut butter and 1 cup powdered sugar; stir in chocolate pieces. Carefully spread peanut butter mixture over crust. Spoon the remaining cocoa mixture over peanut butter mixture; carefully spread to cover. Using tines of a fork, score shortbread into 16 wedges. Bake in 325 degree oven about 50 minutes or till surface looks slightle dry. Cool slightly. While warm, place a chocolate kiss on each wedge. When kiss softens (about 10 minutes), top with a peanut. Score wedges again. Cool completely. Remove sides of pan; cut into wedges.