1. Preheat the oven to 160ºC (350ºF). Grease three 8-inch cake pans and line with parchment paper. You want to have 3 layers (you will have enough batter leftover for a fourth layer if you want.)
2. Melt the butter and chocolate together in a double-boiler or in the microwave.
3. Meanwhile beat together the eggs and sugar for about five minutes at high speed until pale and more than doubled in volume. While you are doing this, the melted chocolate can cool for a few minutes.
4. Add the vanilla to the eggs and beat until combined. Sift in the cocoa and salt and mix again until combined. Stream in the melted chocolate and beat until combined.
5. Divide into prepared cake pans and bake for about 20-25 minutes or until toothpick comes out with some crumbs attached but no longer wet.
6. For the Butter Cream, Use an electric hand mixer to combine all ingredients together in a medium-sized bowl until creamy. This will be enough for a three-layer cake.
7. For the ganache, In a double-boiler or in the microwave, melt and stir the chocolate and butter together until smooth and silky. This ganache will be used in between each layer of the cake, and as the finish for the top. Let cool 10-15 minutes before using, so that it will not melt the buttercream frosting. If the ganache is still slightly warm, it’s okay. You just don’t want it to be hot.
8. To assemble, layer each layer of cake with a layer of slightly cooled ganache, then a layer of buttercream. Finish frosting the cake with the rest of the buttercream and top with remaining ganache. Top with pieces of peanut butter cups, or any chocolates of your choice.
