Preheat the oven to 180C / 350F / Gas mark 4 and prep a 12 hole muffin tin with liners.

In a medium size-mixing bowl using an electric hand mixer or a stand mixer cream together the butter, peanut butter and the sugar until they are well mixed and light and fluffy.

Add the eggs one at a time whisking in-between each addition. More air in the batter at this time will keep your sponge light and fluffy.

Once the eggs are well mixed in add the vanilla extract and whisk again for another minute.

In another bowl mix the flour, baking powder and salt together.

Add a third of the flour to the mix and gently fold in. Then add a third of the milk and fold in. Carry on this way until all the flour mix and milk are all mixed in and well combined.

Carefully put the mixture into your prepared cupcake tins, filling each one no more than two thirds full.

Bake in the centre of your oven for 20 minutes, and if a skewer comes out clean they are done, if not pop them back in for a couple of minutes.

Once they are cooked, take them out of the oven but keep them in their tins for 10 minutes.

After those 10 minutes pop them on a cooling rack to fully cool down.

Beat the butter until it is light in colour, almost white.

Add the milk and vanilla extract to the butter and mix in well.

Sieve in the icing sugar and cocoa powder together and add half of it to the butter mixture.

Once fully combined add the other half of the icing sugar and cocoa powder and mix vigorously.

Generously fill one side of your piping bag with your chocolate buttercream and fill the other side with smooth peanut butter. You want to have a higher ratio of chocolate buttercream to peanut butter.

And swirl on top.