Make the cake:
Preheat oven to 350 degrees Butter and flour a 9 x 13 cake pan.
In a large bowl, whisk the sugar, flour, cocoa, baking powder, baking soda and salt.
In a medium bowl, whisk the eggs, milk, oil and vanilla.
Whisk the wet ingredients into the dry ingredients. Whisk in the boiling water.
Pour the batter (it will be thin) into the prepared pan and bake for about 50 minutes, until a toothpick inserted in the center comes out clean. Let cool in pan.
Reduce oven temperature to 325 degrees.
Invert the cake onto a work surface. Working carefully, slice the cake horizontally.
Make the filling:
Trace a 9 x 13 rectangle onto a sheet of parchment paper and lay it on a large baking sheet.
In a food processor, pulse the almonds with the powdered sugar until the almonds are finely ground.
In a bowl, using an electric mixer, beat the egg whites at medium speed until soft peaks form. Add the granulated sugar and beat until the whites are stiff and glossy, about 2 minutes more.
Using a rubber spatula, fold the almond mixture into the egg whites.
Spread the meringue onto the parchment to fill the rectangle. Sprinkle the chopped peanuts on top.
Bake for about 20 minutes, until lightly browned and firm. Let cool.
In a medium bowl, set in a saucepan of simmering water, heat the peanut butter with the butter and chocolate, stirring constantly until smooth and melted.
Remove chocolate mixture from heat and fold in the Rice Krispies.
Spread the chocolate mixture over the meringue rectangle.
Transfer to the freezer and let cool completely.
Make the ganache:
In a medium bowl set in a saucepan of simmering water, melt the chocolate.
Whisk in the cream until smooth.
Remove from the heat and refrigerate for 1 hour, whisking occasionally, until thick enough to spread.
Assemble the cake:
Place the bottom cake layer, cut side up, on a large board. Spread 1/3 of the ganache over the cake.
Invert the filling onto the cake and peel off the paper.
Spread half the remaining ganache over the filling, then top with the remaining cake layer, cut side down.
Refrigerate until firm, at least one hour.
Using a serrated knife, trim the edges.
Spread the remaining ganache over the top and sides.
Refrigerate to set.
