Chocolate and Peanut Butter Whoopie Pies

Ingredients

1.	Pre-heat the oven to Gas Mark 4 / 180°C / 350°F and line two baking sheets with greaseproof paper
2.	Sift the flour, cocoa, baking powder and salt into a bowl and set aside
3.	In the mixer, cream the sugar and butter together until light and fluffy
4.	Add the eggs a little at a time, ensuring that they are mixed well between each addition
5.	Add a third of the flour mixture and mix until just combined
6.	Mix the vanilla extract into the buttermilk, and add half to the mixture
7.	Add in another third of the flour, followed by the final half of the buttermilk
8.	Add in the final third of the flour, mixing until just combined
9.	Place mixture in a large piping bag with a ½" nozzle. Pipe small mounds of mixture onto the baking sheet about 1½" wide, allowing plenty of space between to spread
10.	Bake for 15-18 minutes, or until the top is puffed up and slightly springy
11.	Cool on the baking sheet for 5 minutes before transferring onto a rack to cool fully
12.	While they cool, prepare the filling
13.	Beat the butter until pale and creamy
14.	Mix in the peanut butter until smooth and well combined
15.	Add in the icing sugar and beat until fluffy. Add in a splash of milk for a slightly softer texture
16.	Using a star shaped nozzle, pipe some of the filling onto one half, starting at the edge and spiralling in to the centre