Preheat the oven to 190°C/375F/Gas 5. Grease 2 x 20cm/8 in loose-based sandwich tins and line the bases with baking parchment.
Put the butter, sugar, flour, cocoa powder, baking powder and eggs into a food processor and blend until smooth and thick. You may need push the mixture down from the sides a couple of times to make sure the mixture is well blended.
Divide the batter between the prepared cake tins and spread it out evenly with a rubber spatula.
Bake for 22–25 minutes or until the cakes are nicely risen and just beginning to shrink away from the sides of the tins. Remove them from the oven and cool for 5 minutes before turning out on to a wire rack. Take off the lining paper and leave the cakes to cool.
When the cakes are cold, cut them in half, horizontally, with a long-bladed serrated knife. Take care to keep the knife parallel to the work surface, to get a good even cut. Place the cakes back on the wire rack or a board, cut sides up.
For the filling, put the jam in a saucepan with the sour cherries and Kirsch and place over a low heat. Bring to a gentle simmer and cook for 6–8 minutes, stirring, until the jam has melted and the cherries are beginning to swell. Leave to cool for 15 minutes.
Sprinkle the cherry brandy over the chocolate sponges, then spread three of them with the sour cherry mixture and leave to cool. Make sure that the sponge without the cherry topping is from the top half of a cake.
Whip 300ml/10fl oz of the cream with an electric hand-whisk until soft peaks form.
Transfer one of the sponges (with the cherry topping) very carefully to a cake stand or plate – slide a cake tin base under the sponge to help you. Using a couple of pudding spoons, dollop about a third of the whipped cream gently on top of the cherry mixture. There is no need to spread it out, but try to keep the spoonfuls evenly spaced over the cake. Sprinkle with a little of the grated chocolate.
Top with another sponge and repeat the layers twice more. You should end up with three layers of sponge, cherries, cream and chocolate. Place the final sponge on top, with its top surface facing upwards.
Whip the remaining 200ml/8fl oz of the cream with an electric hand-whisk until soft peaks form.
Using the flat side of a palette knife, spread about three tablespoons of the cream over the top of the cake, taking it all the way to the edge. Spoon the remaining cream into a piping bag fitted with a large, plain nozzle and pipe rosettes around the edge of the cake. Tip almost all the remaining grated chocolate into the centre and sprinkle the rest over the rosettes.
Decorate with fresh cherries if you have some. Keep the cake cool or chill until ready to serve.
It’s best to eat it the same day as it is made – how could you resist? – but if you need to make the cake in advance, chill it in the fridge for up to 24 hours and allow to stand at room temperature for 30 minutes before serving.
If you can get hold of a jar of morello cherries in syrup, use them instead of the dried cherries. Simply drain off the syrup and add the cherries to the saucepan with the jam. Don’t be tempted to use canned cherries as they have very little flavour. If you can’t get hold of fresh cherries for the decoration, bottledmorello cherries also make a great alternative.