Make the Chocolate Sponge: Preheat your oven to 180°C (160°C Fan). Grease and line a 20cm square baking tin. In a large bowl, cream the butter and sugar together with an electric mixer until pale and fluffy. Beat in the eggs one at a time. Sift the flour, cocoa powder, and baking powder into the bowl and gently fold them in. Finally, fold in the milk. Spoon the batter into the prepared tin and bake for 25-30 minutes, or until a skewer inserted into the centre comes out clean. Let it cool in the tin for 10 minutes before turning out onto a wire rack to cool completely.

Prepare the Cherry Layer: Drain the cherries, reserving all the syrup from both jars in a saucepan (you should have about 500-600ml). Set the cherries aside. In a small bowl, mix the cornflour with 2 tablespoons of the cold cherry syrup to form a smooth paste.

Thicken the Cherry Syrup: Gently heat the remaining syrup in the saucepan. Once it's warm, whisk in the cornflour paste. Continue to cook, stirring constantly, for 3-5 minutes until the syrup thickens and becomes glossy. Remove from the heat and stir in the kirsch and the reserved cherries. Set aside to cool completely.

Start the Custard: In a bowl, whisk the egg yolks, sugar, and cornflour together until pale. Meanwhile, pour the milk and 200ml double cream into a heavy-based saucepan. Add the vanilla paste (or the split vanilla pod). Heat gently until it's just about to simmer – don't let it boil.

Temper and Cook the Custard: Remove the vanilla pod if using. Slowly pour the hot milk mixture over the egg yolks, whisking continuously to prevent the eggs from scrambling. This is a crucial step for a smooth custard. Once combined, pour everything back into the saucepan. Cook over a low-medium heat, stirring constantly with a wooden spoon, for 8-10 minutes until the custard is thick enough to coat the back of the spoon. For more tips, BBC Good Food has a great guide on how to make the perfect custard.

Cool the Custard: Pour the finished custard into a clean bowl. What works best for me is to press a piece of cling film directly onto the surface of the custard to stop a skin from forming. Let it cool to room temperature, then refrigerate until completely cold.

First Assembly: Once all your components are cold, you can begin to assemble. Cut the chocolate sponge into 3cm cubes. Arrange half of the cubes in the bottom of a large trifle bowl (around 3.5-litre capacity). Spoon over half of the cooled cherry mixture, allowing the syrup to soak into the sponge.

Second Layer and Chill: Carefully spoon half of the cold custard over the cherry layer, spreading it to the edges of the bowl to create a clean line. Repeat with the remaining sponge, cherries, and custard. Cover the bowl with cling film and refrigerate for at least 6 hours, or preferably overnight. This allows the flavours to meld beautifully.

Finish and Decorate: Just before serving, whip the 600ml of double cream with the sifted icing sugar until it holds soft peaks. Spoon or pipe the cream over the top of the set custard. Use a vegetable peeler to create shavings from the bar of dark chocolate and scatter them generously over the cream. Top with fresh cherries, if you like.