Chocolate cheesecake

Method

1. Whizz the biscuits into crumbs in a processor, then add the butter and the 1 tablespoon of cocoa. Process again into damp clumps, then tip into a 23cm round springform tin. Press to make an even base and place in the freezer while you make the filling.
2. Preheat the oven to 180°C/fan160°C/gas 4. Melt the chocolate in a bowl, either in a microwave or set over a pan of simmering water, and set aside to cool slightly (see How To… in the Know How section of the website).
3. Beat the cream cheese in a mixing bowl to soften, then whisk in the sugar and custard powder. Beat in the whole eggs, then the yolks and the soured cream. Finally, add the cocoa dissolved in a tablespoon of hot water and the melted chocolate, mixing to a batter. Remove the base from the freezer and line the outside of the tin with a layer of cling film and a layer of foil, to seal it from the water bath. Pour in the filling.
4. Sit the cake tin in a roasting tin and pour just-boiled water into the larger tin to come about halfway up the cake tin. Bake in the oven for 45 minutes-1 hour, until the top of the cheesecake is set and the underneath has a slight wobble.
5. Allow the cake to cool in its tin, then transfer to the fridge to set overnight, covered with cling film.
6. The next day, bring it up to room temperature. Gently melt together the glaze ingredients, then remove from the heat and whisk to a smooth sauce. Cool slightly, then pour on each slice. Serve with a blob of lightly whipped double cream, if you like.