For the cake
Heat the oven to 180°C (160° fan) 350°F gas 4. Grease 3 x 20cm|8" cake tins and line the bases with non-stick baking paper.
Put the butter and chocolate into a small pan and heat gently, stirring, until melted.
Sift together the flour, sugar, cocoa, salt and bicarbonate of soda in a mixing bowl.
Whisk together the eggs and buttermilk.
Stir the melted chocolate mixture and egg mixture into the dry ingredients, then whisk in the hot water until smooth.
Divide the mixture between the tins and bake for 25 minutes, until cooked through. A skewer or cocktail stick inserted into the centres should come out clean. Prick the cakes a few times with a skewer. Mix together the reserved cherry juice and the kirsch and drizzle over the cakes. Cool in the tins for 15 minutes, then place on a wire rack to cool completely.
Reserve a few cherries for the decoration. Mix together the remaining drained cherries and jam.
Heat the cream in a pan just to a boil. Remove from the heat and pour over the chocolate. Stir until melted. Leave to cool and thicken for 30-40 minutes.
Spread 2/3 of the chocolate filling over 2 of the cakes, then spoon over the cherry mixture.
Stack the cakes together. Spread the remaining chocolate cream over the third cake and place on top of the other cakes.
For the chocolate curls
Using a vegetable peeler, scrape thin curls from the chocolate.
Decorate the top of the cake with cherries, chopped white chocolate and chocolate curls.