If you're super-organised, you can make this trifle the day before - the flavours will improve overnight.
950g cherries, pitted (to produce about 800g)
150g caster sugar
200ml dry sherry, plus extra for dipping biscuits
2 tbsp cherry jam
9 sheets gelatine (titanium strength)
10-12 savoiardi biscuits, halved lengthways
50g marzipan, chopped into 5mm pieces
5 tbsp cherry jam, simmered with 3 tbsp water and cooled
250ml pouring cream, whipped
toasted flaked almonds and icing sugar (optional)
1 vanilla bean, split and seeds scraped
150g caster sugar
1/2 lemon, zest finely grated
4 tbsp cornflour
6 egg yolks
450ml pouring cream
Place cherries, sugar and sherry in a saucepan over medium heat. Bring to a simmer, then cook over low heat for 2-3 minutes. Remove three-quarters of the cherries and set aside. Add jam to remaining cherries and simmer for 2 minutes, then strain to produce about 600ml liquid (add water, if necessary, and boil again).
Place gelatine leaves in a bowl and cover with cold water to soften. Squeeze out excess water, add gelatine to cherry mixture and stir to dissolve. Strain half the jelly into a large glass serving dish. Pour remaining jelly into a small dish to 1 centimetre deep. Cover and chill in fridge until set.
Combine vanilla seeds, sugar, lemon zest and cornflour in a large bowl. Whisk in egg yolks. In a medium saucepan, simmer vanilla bean, milk and cream over low heat for about 2 minutes. Remove bean, add milk mixture to egg mixture and stir until smooth. Transfer to a saucepan and stir over low heat until mixture thickens to coat the back of a wooden spoon. Pour into a bowl and chill.
To assemble trifle
Pour a little custard onto jelly in serving dish. Dip 2-3 biscuits briefly in sherry, place on custard and sprinkle with a little marzipan. Spread over a little jam and top with some cooked cherries. Repeat 2-3 times, finishing with custard. Cover with plastic wrap and refrigerate (overnight, if possible).
Cut remaining dish of jelly into small strips. To serve, top trifle with whipped cream, jelly strips, extra fresh cherries, toasted almonds and icing sugar, if using.