Peanut butter frosting
Preheat the oven to 175°C.
Combine the flour and cocoa powder in a bowl and set to one side.
Beat the butter and rich dark brown sugar until pale and creamy.
Add the eggs, vanilla extract, baking powder and salt.
Mix well. Stir in the porridge oats, flour, cocoa powder mixture, and the chopped chocolate.
Form the mixture into small balls 2—3 cm in diameter and place on a parchment-lined baking sheet.Press them slightly with the finger or hand. Bake for about 10-12 minutes.
Leave to cool completely.
Frosting Put the room temperature butter, icing sugar, milk and salt in a bowl. Beat together until the frosting is fluffy and creamy.
Place about 1 tsp of frosting in the middle of one cake, spread it out a little, and place a second cake on top. Press the cakes together carefully so that the filling just comes to the edges.