Preheat your oven to 180℃ (160℃ for fan ovens) and line a cupcake tin with 12 cases.
In a large bowl, cream together the butter and sugar until soft and fluffy. Stir in the vanilla extract.
Mix in the flour and the eggs, a little bit at a time, until you have a smooth, thick cake batter. If it's too thick, you can add a splash of milk to help loosen it.
Divide the cake mix between your 12 cases. Gently push a chunk of Milky Bar chocolate into the centre of each one.
Bake for 20-25 minutes until a toothpick comes out clean. Transfer them to a wire rack and leave to cool completely.
Milky Bar buttercream:
Melt the Milky Bar chocolate and set aside to cool completely.
Add the butter to a large bowl and stir in the icing sugar a little bit at a time. Then stir in double cream.
Fold in the cooled Milky Bar chocolate and mix until smooth. Transfer the buttercream to a piping bag fitted with a star nozzle and pipe a swirl onto each cupcake.
Top with chunks of Milky Bar chocolate and Milky Bar buttons and enjoy!