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 milk in a saucepan until steaming. Whisk egg yolks with sugar and cornstarch in a separate bowl. Gradually pour hot milk into 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 cool completely.
03 - Combine mixed berries with sugar and lemon juice in a bowl. Let stand for 10 minutes to allow berries to release their juices and become slightly syrupy.
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, then spoon in half the macerated berries. Add half the whipped cream. Repeat layers with remaining cake pieces, 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.