Preheat the oven to 180°C (350°F) and grease and line with grease-proof paper the base of a 20cm loose-bottomed or springform cake tin.
For the sponge: Separate the eggs and whisk the yolks with the sugar in a large bowl until moussey, pale and thick – a good couple of minutes. Sieve over the cocoa powder and a pinch of salt and fold in.
Whisk the whites in a separate clean bowl, until stiff but not dry. Robustly stir in a little of the whites into the yolk mixture to loosen it, then fold in the rest very gently until just combined, so you knock as little air out as possible. Carefully spoon into the tin, smooth the top and bake for 35-40 minutes, until puffed up and set on top. Leave to cool completely in the tin; it will sink slightly, but that’s normal.
For the filling: Drain the cherries, retaining the syrup. Mix 100ml of it with the kirsch and put aside.
Cut the cooled cake into three horizontal slices and put on separate plates. Spoon or brush half the syrup over the slices and leave to sink in; you can add more if it is all absorbed, but don’t overload it.
Whip the cream until thick, then sift in the icing sugar and add the vanilla extract. Whisk until voluminous, but not too stiff to spread.
When you’re ready to assemble the cake, set aside about 12 cherries for decorating the top of the cake. Put the bottom sponge layer onto a serving platter (be gentle as you lift it) and slather on half of the jam, half of the remaining cherries and a third of the cream. Put the second layer of sponge over top; add the rest of the jam, the rest of the remaining cherries, and the second third of cream. Put on the final layer of sponge; use a palette knife to spread the remaining cream on top. Grate chocolate curls generously over them, and arrange the remaining cherries around the edge.
Chill for an hour before serving.