Bake the cake according to the directions on the package.

Make 2 8" round cakes.

Cool cakes in pans on cooling rack for 15 minutes.

Remove cakes from pans and place on cooling rack, allow to cool completely. (At least 45 minutes)

In a large bowl mix together the peanut butter and 1 cup of confectioner's sugar.

Add in the second cup of confectioner's sugar, it will become crumbly.

Add in the vanilla and 1/4 cup of the heavy cream.

Once that is fully incorporated and another 1/4 cup of heavy cream. Mix until smooth.

Slowly add in the remaining heavy cream until it becomes the consistency you want it to be.

If your cake isn't flat on top, carefully slice off the domes portion so that your layers will stack evenly.

Use a turntable and a long, sharp knife to cut each cake into two even layers

Place the bottom layer in the center of the plate or cake board.

Cover that layer with a layer of the peanut butter filling.

Repeat the layering process, making sure your layers are even, until all four cakes are layered and there is peanut butter between the layers. DO NOT put peanut butter on the top layer.

Place the chocolate and butter in a heatproof bowl set over a saucepan of hot water. Stir occasionally with a wooden spoon until melted.

Add the egg and beat until smooth. Remove the bowl from the saucepan. Stir in the confectioner's sugar and beat until smooth and glossy.

Pour immediately over the cake for a smooth finish. You may need to use a knife or the back of a spoon to help coat the sides with the icing.