Preheat your oven to 170ºc / 160ºc fan and grease and flour, or cut mini circles and line the bottoms of your cups in your 12-hole mini sandwich tin!
Cream together the butter/spread and light brown sugar with an electric beater until smooth – add in the beaten eggs, flour, cocoa powder and vanilla and beat again for about about 20-30 seconds on a medium speed.
Spoon into your tin evenly per cup and bake in the oven for 16-18 minutes or until cooked through! Leave to cool on a wire rack.
Once the cakes are cool, make the frosting – beat the softened butter until smooth – this can take a couple of minutes.
Add in the icing sugar and cocoa powder 1/3 at a time, making sure the sugar is fully incorporated each time until moving on.
Keep on beating the frosting but add the vanilla, and then add 1 tbsp of boiling water at a time till you reach your desired consistency. I usually use about 1-2 spoonfuls.
Cut each cake in half carefully – using a piping bag, pipe on some buttercream for each cake and then add the other half of each mini cake on top.
Decorate your cupcakes how you like – I melted over some white chocolate, milk chocolate and then some sprinkles.