Preheat the oven to 350F (175C ) degrees and line up 4 (6-inch or 15cm) cake tins with parchment paper.
In a bowl of a stand mixer, cream together the eggs, sugar and vanilla extract. Mix until you get light, double in size creamy mixture. Then add the light cooking oil and mix shortly one more time. In the end add the flour, cocoa powder, and baking powder and mix shortly on low speed just to combine everything.
Divide the batter evenly among the cake pans. Smooth the batter evenly into each pan with the back of a spoon.
Bake the cakes on 350F (175C ) for about 15 minutes, or until a toothpick inserted into the middle comes out with only a few crumbs attached.
Allow cakes to cool in the pan for 10 minutes and turn out onto a wire rack to cool completely before frosting.
To make the peanut butter frosting
Using a handheld or stand mixer fitted with a whisk attachment beat the softened butter on medium speed for 2 minutes until completely smooth and creamy. Add the peanut butter, confectioners’ sugar, heavy cream, vanilla extract, and salt with the mixer running on low. Increase to high speed and beat for 4 minutes. Add up to 1/4 cup more confectioners’ sugar if frosting is too thin or another Tablespoon of cream if frosting is too thick.
Assemble the cake
Place one cake layer on your cake stand. Spread a generous, about 3/4 cup, frosting over top of the first layer, then sprinkle a little bit crushed salted peanuts. Put the next sponge on top and repeat the same step. Then put the last sponge on top and spread the remaining frosting all over the top and the sides of the cake.
To Make the Chocolate Ganache
Put the dark chocolate in a bowl and heat the cream in a small pan until just steaming. Pour the cream over the chocolate and leave to melt for 5-10 mins. Stir to make a glossy ganache, then set aside to firm up a little – you want the ganache to be pourable but not too runny, to make drizzly droplets down the side of the cake.
When the ganache is the correct consistency, remove the cake from the fridge and spoon the ganache over the top edge of the cake. Fill in the middle of the top of the cake with chocolate too.
Optionally, make pipes on top of the cake with the remaining peanut butter frosting and decorate with the remaining salted peanuts.
The cake is best served within 2-3 hrs of assembling, but will still taste delicious for up to 3 days. Store leftovers in the fridge and allow to come back to room temperature before serving.