Soak the cherries in the kirsch while you prepare the other elements.Preheat the oven to 180C/160C fan/gas mark 4. Line a 20cm x 25cm tin with greaseproof paper.
Make the brownie. Melt the chocolate with the butter in a bowl over a simmering pan of water – or use a microwave set on medium using 10-second blasts until the chocolate is melted.
Using an electric mixer, beat the sugar with the eggs until pale and voluminous. Carefully fold in the flour and cocoa powder, mixing to combine, then add the melted chocolate and butter mixture, stirring to combine. Pour the brownie mixture into the lined tin and bake in the oven for 25 minutes.
Remove from the oven when the top is crisp and the centre is cooked through – you want the finished brownie to be cake-like, and not too gooey when assembling the trifle. Set aside to cool.
Take one heaped tablespoon of the custard and mix it with the drinking chocolate to form a smooth paste. Then incorporate this into the remaining custard, mixing well.Get a large trifle bowl ready, at least 30cm in diameter.
Roughly chop up the cooled brownie and distribute in the bottom of the bowl. Add the kirsch-soaked cherries and mix through any leftover kirsch with the jam to loosen it, before spooning the jam over the brownie and cherries.
Add the chocolate custard. Chill for at least 30 minutes in the fridge for the custard to settle.
Whip the cream with the icing sugar to form soft peaks then top the custard with the sweetened cream. Sprinkle over the grated chocolate and gold leaf to decorate. Refrigerate until ready to serve.