Preheat oven to 190°C (170°C fan) mark 5. Grease and line base and sides of a 20.5cm (8in) round cake tin with baking parchment.

Put eggs and caster sugar into a large non-metallic bowl. With a handheld electric whisk, beat to combine. Set bowl over a pan of gently simmering water and whisk until mixture is pale and thick – about 5min. Take bowl off heat and continue whisking until cool – about 3-5min.

Sift in flour and cocoa powder and fold together with a large metal spoon, trying not to knock out air. Carefully pour into tin, level and bake for 20-25min until risen and springy to the touch. Remove from tin and leave to cool on a wire rack.

Meanwhile, put custard and chopped chocolate into a small pan and heat gently, stirring occasionally, to melt chocolate. Set aside.

Drain tinned cherries, reserving 4tbsp of the syrup. Mix Kirsch into reserved syrup. In a separate bowl, mix jam into the cherries. Set both aside.

To assemble, in a large bowl whip cream and icing sugar until cream just holds its shape. Mix a large spoonful of whipped cream into chocolate custard to loosen. Slice cooled cake horizontally into three even layers.

Place one sponge layer in base of a large trifle bowl (trim sponge if necessary). Brush over ⅓ of the Kirsch syrup. Top with half the cherry jam mixture, then spread over half the custard, followed by ⅓ of the cream. Repeat layering process once more, finishing with a final layer of sponge (brushed with remaining syrup) and cream. Decorate with fresh cherries, if using, and grated chocolate.