Preheat the oven to 170C/325F/Gas 3. Line a 12-hole muffin tray with paper cases.
Beat the butter and sugar together in a bowl until light and creamy. Gradually add the eggs, one at a time, until well combined. Sift in the flour and cocoa powder and mix until well combined. Fold in the milk and melted chocolate.
Spoon or pipe the mixture into the muffin cases and bake for 18-20 minutes, or until well risen and springy to the touch.
Remove the cakes from the tin and set aside to cool on a cooling rack. Drain the cherries in a sieve collecting the kirsch in the bowl below. Pierce the cakes with a skewer and carefully pour about a teaspoon of the kirsch over each cake.
Heat the kirsch and arrowroot paste in a small saucepan until just boiling. Remove the pan from the heat and beat until thickened.
Using a small knife make a well in the top of each cake by removing a disk of cake
Pipe or spoon a swirl of cream onto the cakes, top with a few cherries and drizzle with the thickened kirsch. Just before serving, grate over some chocolate.