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 for added moisture and flavor.
02 - Heat whole milk in a saucepan until steaming. Whisk egg yolks with granulated sugar and cornstarch in a separate bowl until smooth. Gradually pour hot milk into the yolk mixture while whisking constantly to temper the eggs. Return everything to the pan and cook over medium heat, stirring continuously, until thickened. Remove from heat and stir in vanilla extract. Allow to cool completely.
03 - Combine mixed berries with granulated sugar and lemon juice in a bowl. Stir gently and let sit for 10 minutes to macerate, allowing the berries to release their natural juices.
04 - Beat heavy cream with powdered sugar and vanilla extract using an electric mixer or whisk 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 cubes, 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 and layers to set.