How to Make It
Preheat the oven to 350°. Butter and flour a 9-by-13-inch 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.
Invert the cake onto a work surface. Working carefully, slice the cake horizontally. Reduce the oven temperature to 325°.
Trace a 9-by-13-inch rectangle onto a sheet of parchment paper and lay it on a large baking sheet. In a food processor, pulse the almonds with the confectioners' sugar until they're 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. Using a rubber spatula, fold in the almond mixture. Spread the meringue on 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 milk chocolate, stirring constantly, until smooth and melted. Remove from the heat and fold in the Rice Krispies. Spread the mixture all over the meringue rectangle. Transfer to the freezer and let cool completely.
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.
Place the bottom cake layer cut side up on a large board. Spread one-third of the ganache over the cake. Invert the filling onto the cake and peel off the paper. Spread half of the remaining ganache over the filling, then top with the second cake layer. Refrigerate until firm, at least 1 hour. Using a serrated knife, trim the edges. Spread the remaining ganache over the top and sides of the cake and refrigerate to set. Cut and serve.