In large saucepan over low heat, beat peanut butter, sugar and corn syrup until blended and sugar has dissolved. Remove from heat, stir in rice cereal and cornflakes. Press into lightly greased (" square cake pan; let cool. Filling: In bowl, beat icing sugar and butter; beat in cream and vanilla. Spread over cereal base, chill for 30 minutes. Topping: In double boiler, over hot water, melt chocolate and butter, let cool. spread evenly over filling, chill for 20 minutes. Cut into squares. (Can be refrigerated for up to 1 week or frozen up to 1 month. Let soften slightly before serving.) MAKES: 36 SQUARES