Directions

1. The cake and stars are best made a day ahead (the cake is easier to slice and fill, and the stars have time to set). Heat oven to 160C/fan 140C/gas 3. Butter and base-line a deep loaf tin (22 x 11 x 6cm). Put the chocolate and butter for the cake in a saucepan. Mix the coffee with 50ml water, then pour into the pan. Warm through over a low heat, just to melt - be careful not to overheat.
2. While the chocolate melts, mix both flours with the bicarbonate of soda, both sugars and the cocoa. Break down any lumps in the sugar with your fingers. Beat the eggs, then stir in the soured cream. Pour this and the melted chocolate over the flour mixture, then stir everything together - the mix will be very soft. Pour it into the tin, then bake for about 1 1/2 hrs, or until firm on top. Let the cake cool in the tin (it may crack if you turn it out too soon), then loosen the sides and carefully turn it out onto a wire rack to cool completely.
3. To make the stars, line a baking sheet with baking parchment. Melt both chocolates separately. Pour and spread the white chocolate thinly into a rectangle on the parchment. Drizzle the dark chocolate off the end of a teaspoon in bold squiggles over the top. Leave in a cool, dry place (not the fridge) until almost set but not hard, then lightly press down with a star cutter, about 5.5cm across, to make at least 6 star outlines. (Make a few extra in case of breakages and wipe the cutter each time you press a star shape.) When completely set, cut through the star outlines with a small sharp knife, then carefully lift them off onto baking parchment.
4. For the white chocolate icing, heat the cream just to boiling. Remove from the heat, tip in the chocolate and swirl so it starts to melt, then pour in the boiling water and stir to melt completely. Pour into a small bowl and chill in the fridge for about 1 hr to cool and thicken slightly. Beat with an electric hand mixer until thick and glossy.
5. When the cake is completely cold, place it into the fridge to chill (this makes it easier to slice). Take the cake out of the fridge and turn it over so the flat base becomes the top of the cake. Slice the cake horizontally into three. Sandwich back together with the white chocolate icing, not quite up to the edges. (This can be done a day ahead and chilled.)
6. For the dark chocolate icing, heat the cream with the sugar just to boiling. Remove from the heat, tip in the chocolate, then stir in the boiling water. Leave to cool and thicken a little. Put the cake on a wire rack with parchment paper underneath (to catch any drips). Pour and spread the icing all over the cake. Leave to set slightly, then arrange the truffles down the centre and prop 5 or 6 of your best stars against them.