Cut the rim from the sponge cases. Line the base of a 20cm cake tin with the first sponge. Brush with 6 tablespoons of the reserved cherry syrup.
Divide the cherries into three. Arrange one third around the edge of the sponge. Fold one third of the remaining cherries into 600ml of the cream with the chocolate and icing sugar.
Spoon half of this mixture over the centre of the sponge and level with a pallet knife or the back of a spoon.
Top with the second sponge, pushing it down on top of the creamy layer. Brush with 4-6 tablespoons of the syrup and arrange the final third of cherries around the sponge rim. Top with the remaining cherry and cream mixture.
Press the final sponge firmly in place. Brush liberally with 4-6 tablespoons of syrup.
Chill for 30 minutes. Run a warm knife around the inside of the tin. Release the spring form clip and push the cake up and out.
Lift the cake on to a serving plate and decorate with spoonfuls of the remaining whipped cream. Top with any remaining cherries and grated chocolate.