Prepare Chocolate Cake and cut into 3 layers.
To make filling and decoration, whip cream with half the powdered sugar until stiff; divide into 3 portions.
Add remaining powdered sugar and cocoa powder to 1 portion; spread over bottom cake layer.
Halve peach slices and arrange all but 2 slices over second cake layer.
Mix second portion of whipped cream mixture with maraschino; spread over peaches.
Top with third cake layer.
To make frosting, melt chocolate with powdered sugar, water and butter in a double boiler over low heat.
Stir until smooth; spread evenly over top and sides of cake.
Cool.
Put remaining whipped cream mixture into a pastry bag fitted with a fluted nozzle.
Decorate cake with swirls of piped cream, reserved peach slices cut into segments and pistachios.