Heat oven to 180C/160C fan/gas 4. Grease and line the bases of 6 dariole moulds with baking parchment. Put the butter, sugar, egg, flour, ground almonds, bicarbonate, cocoa and Guinness in a mixing bowl. Beat together until lump-free. Divide between the tins then bake for 20-25 mins until risen and a skewer poked in comes out clean. Cool for 15 mins, then remove from tins and cool completely - the same way up they baked, don’t turn upside-down.
Whip cream with the icing sugar and splash of Champagne, if using, until thick. Spoon a dollop onto the top of each cake and dust with a touch of cocoa. Serve with glasses of Champagne or Black Velvets for pudding.