Line two large baking trays with baking paper. Put the icing sugar, almonds and cocoa in a food processor and blend to a very fine powder. Sieve the mixture into a large mixing bowl and add half the egg whites. Combine with a fork to make a wet dough.
Add the remaining egg whites to the freestanding mixer bowl. Heat the granulated sugar and 50ml/2fl oz water in a small pan over a medium heat, stirring occasionally until the sugar dissolves. Stop stirring and bring the mixture to the boil with the sugar thermometer submerged. Once the syrup reaches 112C, start the stand mixer on a high speed. When the syrup reaches 118C the egg whites should be foamy and white. Carefully pour the boiling syrup down the side of the mixing bowl with the stand mixer running (CAUTION: Sugar syrup is very hot. Do not pour the syrup onto the beaters or it may splash back at you.). Keep whisking the meringue until the outside of the bowl is cool to the touch.
Using a soft spatula, mix half the meringue into the almond mixture – don’t worry about being too gentle. Once the colour is uniform, add the remaining meringue.
Spoon the mixture into a large piping bag and cut a 1cm/1/2in diameter hole in the tip. Pipe 3cm/1¼in discs onto the prepared baking trays and leave at room temperature for at least half an hour before baking. This allows a skin to form, which helps achieve a good dome.
Preheat the oven to 170C/150C Fan/Gas 3. Just before the trays go into the oven, sharply drop them from a small height onto the work surface – this helps the “foot” of the macaroon grow when it bakes. Bake for 14-15 minutes. Remove the macaroons from the oven and leave to cool on their trays.
Meanwhile, make the ganache. Put the chocolate in a small heatproof bowl. Heat the cream in a saucepan until it starts to steam (but before boiling). Pour the cream over the chocolate and leave for a minute. Gently stir until the chocolate melts and the ganache becomes glossy. Add the kirsch, if using, and stir. Set aside to firm-up to a piping consistency.
Transfer the ganache to a small piping bag and cut a small hole in the tip. Place a blob of cherry jam in the centre of each shell and pipe a ring of ganache around it. Place the other half-shell on top and squeeze gently until the ganache reaches the edge. Repeat with the remaining shells.