Preheat the oven to 180C/Gas4; line a 12-hole muffin tin with cupcake cases
Sift the flour, cocoa and ½ tsp salt into a mixing bowl then stir in the sugar; beat in the soft butter; combine the soured cream, eggs and vanilla together in a separate bowl then mix into the cake batter until smooth; divide between the cases
Bake in the oven for 30-35 minutes until firm; cool on a wire rack
To make the frosting, beat the butter, icing sugar, milk and vanilla extract until smooth and fluffy; place the marshmallows into a bowl and microwave for 30-60 seconds until the marshmallows are just melted; add the melted marshmallows to the frosting and beat again until smooth; chill the frosting in the fridge to firm up for about 45 minutes
For the bunny ears, cut each marshmallow in half on the diagonal from top to bottom; place the pink sugar in a plate and press the cut side of the marshmallows in the sugar
To decorate, place the frosting in a piping bag with a plain 1-5cm nozzle and pipe on top of the cooled cupcakes; add the ears, eyes and teeth to each cupcake and continue to decorate with the chocolate icing
12 servings