Preheat the oven to 170C/325F/Gas 3.
Lightly butter a 20cm (8in) loose-bottomed cake tin then dust with a little plain flour and shake off any excess. Line the tin with greaseproof paper.
For the cake, place butter and sugar in a bowl and whisk until light and fluffy. Beat in the eggs one at a time then fold in the flour and the cocoa powder.
Spoon the mixture into the prepared cake tin, smooth the surface with a knife and bake in the pre-heated oven for 1 hour -1 hour 45 minutes until firm and springy. To test if the cake is done, insert a clean skewer into the middle of the cake - if it comes out clean then the cake is ready.
Remove from the oven and leave to cool in the tin for five minutes before turning out onto a wire rack.
Drain the cherries, reserving 200ml (7 fl oz) of the cherry syrup. Add the kirsch to the reserved syrup.
Use a large serrated knife to slice the cake horizontally into three equally sized rounds.
Place each round on a chopping board and spoon the cherry syrup evenly over each disc and leave to soak in.
For the icing, heat 200ml (7 fl oz) of the double cream to scalding point then add the chocolate pieces. Remove from the heat and stir gently until the chocolate is melted and smooth. Pour into a bowl and allow to cool in the refrigerator, to thicken slightly.
Whip the remaining double cream until thick. Spread one of the cake discs with half of the cream then cover with half of the cherries, pressing them in lightly. Top with the second disc of sponge and repeat this process, finishing with the third disc left plain on top. Gently press the whole cake together with the palms of your hands.
Remove the chocolate icing from the fridge and give it a quick stir. Use a palette knife to thickly spread the top and sides of the cake with the icing, starting with the top first. This way, if the chocolate oozes down the sides of the cake, it won't matter. (If preferred you can leave the sides of the cake without icing to show off the layers.)
Leave the cake to set in a cool place then slice into large wedges and serve.