Black forest ‘forest’ trifle

Method

1. For the custard, pour the milk and cream into a pan. Put over a medium heat and warm through, stirring every now and then to stop it catching. In a large bowl, use a balloon whisk to beat the egg yolks and sugar together until combined and a little paler. Once the milk is steaming hot and quivering (but not quite boiling), gradually pour it into the egg mixture, whisking constantly until combined.
2. Pour the mixture back into the pan and put over a low-medium heat. Use a rubber spatula to gently stir the mixt as it heats through (you don’t want to add bubbles of air). Cook gently until the custard thickens enough to coat the back of the spatula (about 5 minutes). It should reach 82°C when it’s ready. To check, dunk the spatula in the custard then push a finger across it – if the line you’ve created holds for a few seconds it’s ready. Put the chopped chocolate in a heatproof bowl, then pour the custard over. Leave for 1 minute to melt, then stir to make a chocolate custard. Leave to cool, cover with baking paper touching the surface and chill for at least 2 hours.
3. For the cake, heat the oven to 150°C fan/gas 3½ and grease and line the cake tin base with oil and baking paper. Melt the chocolate in a heatproof bowl over a pan of just simmering water (don’t let the bowl touch the water), then leave to cool slightly. In a large bowl, combine the flour, cocoa, sugar, baking powder and a pinch of salt. In a jug, whisk the 2 tbsp oil and the egg until combined, then stir in the soured cream. Pour the wet ingredients and melted chocolate into the dry, then stir to combine. Pour in 40ml just-boiled water (you can use the water from the pan used to melt the chocolate) and mix. Tip the batter into the prepared tin, then bake for 16-18 minutes until a skewer pushed into the centre comes out with only a few damp crumbs. Set the tin on a wire rack to cool.
4. Put the frozen cherries, icing sugar and brandy or kirsch in a small pan over a medium heat. Cook for 5-6 minutes until syrupy but the cherries are still holding their shape. Set aside to cool.
5. Whizz the bourbon biscuits in a small food processor or crush with a pestle and mortar to make crumbs that look like soil.
6. When you’re ready to assemble, prepare the cream. Put the double cream and icing sugar in a bowl and whisk to soft peaks (that flop over when you remove the whisk), then fold in the soured cream.
7. Remove the cake from the tin and cut into 6 wedges. Arrange the wedges in a circular shape that mirrors the shape of the baked cake (cutting it into wedges helps it fit the bowl). Spoon over another splash of booze, then top with the cherry mix. Spread with the chocolate custard, then top with the cream. Chill for 30 minutes (or up to 24 hours if making ahead).
8. When you’re ready to serve, scatter over the bourbon crumb. Carefully remove some leaves from the tops of the rosemary sprigs, then turn upside down and poke the leaf-free ends into the bourbon ‘soil’ so they look like Christmas trees. If you like, spray with edible glitter or decorate with gold leaf.