01 - Cube the sponge cake or ladyfingers and arrange half in the base of a large trifle dish. Sprinkle with orange juice or sherry, if using, to moisten the cake layer.
02 - Heat the milk in a saucepan until steaming. Whisk egg yolks with sugar and cornstarch in a separate bowl until pale. Gradually pour hot milk into the yolk mixture while whisking constantly. Return everything to the pan and cook over medium heat, stirring continuously, until thickened. Remove from heat, stir in vanilla, and let cool completely.
03 - Combine mixed berries with sugar and lemon juice in a bowl. Let sit for 10 minutes to release natural juices and enhance flavor.
04 - Whip heavy cream with powdered sugar and vanilla extract until soft peaks form. Be careful not to overwhip.
05 - Layer half the custard over the cake base, followed by half the macerated berries, then half the whipped cream. Repeat layers with remaining cake, custard, berries, and whipped cream, ending with whipped cream on top.
06 - Decorate the top with chocolate eggs, colored sprinkles, and fresh mint leaves if desired. Refrigerate for at least 2 hours before serving to allow flavors to meld.