Preheat oven to 190 C/ 170 fan/ 375 F/ gas mark 5 and line a 12 hole muffin tin with paper cupcake cases.
Sift together the flour, bicarbonate of soda and sugars together in a large mixing bowl.
Melt the cocoa powder, water and butter over a low heat in a small saucepan. Do not allow this mixture to boil.
Mix the milk and vinegar together and set aside a few minutes to curdle.
Add the chocolate mixture, the milk, egg and vanilla to the dry ingredients and whisk until thoroughly combined. The batter will be thin.
Spoon into the prepared baking cakes and bake in the centre of the oven for 20 minutes, until well risen and springy.
Leave to cool for five minutes in the tin and then squeeze in the Dr. Oetker cupcake filler. Transfer to a wire rack to cool completely.
To prepare the masquerade masks find an image online that you like and print out an A4 sheet with 12 copies of the image on it.
Break the chocolate and melt in a heatproof bowl suspended over a pan of barely simmering water.
Place a clear silicone mat (or waxed paper) over the printout of the masks and spoon the chocolate into a piping bottle fitted with a small nozzle. Carefully draw over the paper mask template. Set aside in a cool place for at least an hour to harden (don't refrigerate them as they will attract condensation at room temperature).
To prepare the frosting beat together all the ingredients until light and creamy. Frost the cupcakes using a large star nozzle and sprinkle over the gold sprinkles, if using.
Arrange a chocolate masquerade mask on the top of the cupcakes and serve!
Mum of three, daydream adventurer, OU Life Sciences graduate, occasional crafter, ex-pat Canadian & quite possibly Britain's most northerly food blogger.