For the cupcakes: heat the oven to 160°C (140° fan) 325°F gas 3. Place paper cases in a 12 hole bun tin..
Stir together the flour, cocoa, bicarbonate of soda and salt in a mixing bowl. In another bowl mix the buttermilk, vinegar, vanilla and red food colouring.
Beat the butter and sugar together until pale and fluffy. Beat in the egg a little at a time. Mix in 1/3 of the flour mixture, followed by half the buttermilk mixture, then another third of the flour, the remaining buttermilk and finally the last of the flour mixture.
Spoon into the paper cases. Bake for about 20 minutes, until risen and springy to the touch. Place on a wire rack to cool completely.
For the topping: melt the chocolate and butter in a pan over a very low heat. Remove from the heat, stir in the vanilla and leave to cool and thicken.
Spread the topping over the top of the cakes and decorate with chocolate flakes and mini sugared chocolate eggs