100g chopped dark chocolate, plus extra to decorate
Heat the oven to 180c/fan160c/gas4. Line and butter 2 x 18cm sandwich tins. Beat the cake ingredients (not the double cream) together in a bowl, add the milk if the mixture is too stiff – it should drop off a spoon when tapped. Divide the mixture between the tins and level the tops.
Bake on the same shelf for 20-25minutes or until the sponges are risen, slightly shrunk away from the edge of the tin and spring back when lightly pressed. Leave to cool for 5 minutes then turn out onto a rack and peel off the paper. Cool completely before filling.
To make the icing, melt the butter and chocolate together in a microwave, or in a bowl set over a pan of simmering water. Stir well, then leave until it’s cool enough to spread easily and will run a little.
Whip the cream and use it to sandwich together the cakes. Spread chocolate ganache over the top of the cake, letting some run over the edge. Decorate with chocolate curls.