This is undeniably a rich cake; to really appreciate its full flavour it is important to use a good-quality dark chocolate. A small slice is enough – serve it with extra-thick double cream or crème fraîche. It keeps well for a few days.
400g/13oz good-quality chocolate
300g/10oz unsalted butter
10 eggs, separated
225g/7 oz caster sugar
Preheat the oven to 180C/350F/Gas4.
Melt the chocolate and butter together in a bowl over a simmering pan of water. Remove the bowl from the pan and allow to cool slightly. Add the yolks one at a time, beating after each addition, followed by the sugar.
Whisk the egg whites in a large clean bowl until stiff peaks appear – you can do it in an electric mixer if you prefer. Once the whites are whipped, fold them into the chocolate mixture a third at a time.
Pour the mixture into a 10-inch cake tin with a removable bottom and place on the middle shelf of the oven. Cook until the cake is slightly set and risen like a soufflé.
Remove from the oven and sit to cool on a wire rack for 10 minutes before placing a heavy plate on the top – this will squash the cake.
Allow to cool completely, then remove the plate and turn the cake out on to a large round plate. Serve in smallish slices, passing the cream around for all to help themselves.