.Melt the chocolate and butter in a heatproof bowl over a pan of barely simmering water (the bowl shouldn’t touch the water), stirring until smooth. Remove from the heat, cool slightly, then whisk into the chestnut mix. Stir in the egg yolks one at a time, along with the flour mixture.In a separate bowl, beat the egg whites until stiff. Slowly add the sugar a little at a time until glossy. With a metal spoon, fold a third of the egg whites into the cake mixture to loosen it, then fold in the rest until just combined. Drain the raisins, then fold them in too.Scrape the mixture into the prepared tin and smooth the top. Bake for 30-35 minutes until a few crumbs cling to a toothpick pushed into the middle. Let the cake cool in the tin for 10 minutes, then remove to a rack. 6 When the cake is completely cool, flip it over on the rack and peel off the baking paper – this is now the top of the cake. For the ganache, put the chocolate in a heatproof bowl. Warm the cream until steam just appears on the surface – if it gets too hot, the ganache might split.Pour the cream over the chocolate, leave for a minute, then stir gently with a rubber spatula until smooth. Leave for 5 minutes to thicken slightly, then slowly pour it over the cake (put some baking paper underneath the rack it to make it easier to tidy up and scoff some of the excess ganache). When the ganache has set, decorate as you wish. Don’t hold back.
