Put all of the ingredients into a large bowl (100g self-raising flour, 20g cocoa powder, 115g caster sugar, 2 large eggs, 115g soft margarine, ¼ tsp vanilla extract, 1 tsp milk and the grated chocolate) mix on a low speed until fully combined.
Divide the mixture evenly between the cupcake cases.
Put the tin in the oven and cook for 25-30 minutes until a skewer inserted in the middle comes out clean.
Once cooked, remove the cakes from the tin and leave to cool on a wire rack while you make the caramel buttercream.
Put the buttercream ingredients into a large bowl (150g butter, 150g caramel sauce, 150g icing sugar) and beat on a low speed until fully combined and smooth.
Build the cupcakes
Use a pestle and mortar or rolling pin to crush the shortbread biscuits.
Use a teaspoon to scoop out the centre of each cupcake.
Add 1tsp of caramel sauce and then 1 tsp of crushed shortbread into the centre of each cupcake.
Put the caramel buttercream into a piping bag fitted with a star nozzle and pipe the buttercream on top of each cupcake.
To finish sprinkle each cupcake with a little of the crushed shortbread.
Nutritional information is not provided as you probably don't want to know - it's quite a bit of running!