Preheat oven to 180 C / Gas 4. Line a 9" (23cm) spring-form cake tin with baking parchment.
Melt butter and chocolate in a dish over hot water. Whisk the egg whites until it peaks. In a separate bowl, whisk yolks and sugar until frothy. Mix in melted chocolate and butter. Add sifted flour, cornflour and baking powder, mix until combined. Gently fold in egg whites until just combined. Pour into spring-form and bake for 40-45 minutes. Cool on a wire rack.
Filling: Mix cornflour and sugar with some cherry juice. Add remaining cherries and juice to a pan and boil until reduced to a pulp. Add kirsch and thicken with cornflour mixture. stir well allow to cool slightly. Should be like jam.
Meanwhile take the cool sponge and enough strong thread to go 1 1/2 times round cake. Place thread around sponge 1/3 from top crossing at front, holding both ends pull thread to cut through sponge. Repeat this for another layer. You should now have 3 layers. Carefully separate them, placing the bottom layer on a plate.
Soak all layers with Kirsch (underside of top). On bottom and middle layer spread over with warm jam mixture. Allow to cool and set.
Whip cream and sugar until stiff. Spread 1/4 of cream on top of jam on bottom layer. Carefully place middle layer jam side up on top of bottom.
Repeat with cream. Place top on cake and cover whole cake with cream, keep some cream for piping dollops. Sprinkle with chocolate shavings. Pipe a dollop for each portion around the edge and top with glace cherries.