Heat oven to 190C/fan 170C/gas 5. Butter and line a 30 x 35cm (or thereabouts) Swiss roll tin. Using an electric hand-held beater, whisk the eggs and sugar until they are thick and pale and the mixture leaves a trail when the beaters are lifted. This will take about 5-6 mins.
Sift the cocoa powder and flour over the mixture, then fold in using a large metal spoon. Drizzle over the butter, then fold this in, too. Pour the mixture into the tin and gently level and smooth out with a palette knife. Bake for 10-12 mins, until the cake feels firm to the touch and springs back when lightly pressed.
Turn the cake out onto a cooling rack and peel off the paper. Leave to cool. Meanwhile, select and reserve 6 cherries with stalks (to decorate), then stone the remainder. Whip the cream until it just holds its shape.
Cut 12 rounds from the cake using a 7-8cm cutter or a glass, then sprinkle each with a tsp of kirsch. Set 6 cakes on a large plate or stand, spread with cream, then arrange the stoned cherries on top. Top with a second circle of sponge. Spread with the rest of the cream, sprinkle with chocolate, then set a cherry on each cake and serve.