01 - Cube the prepared 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 pale and thick. Gradually pour hot milk into the yolk mixture while whisking constantly to prevent curdling. Return everything to the pan and cook over medium heat, stirring continuously, until thickened and bubbly. Remove from heat, stir in vanilla extract, and cool completely before layering.
03 - Combine mixed berries with granulated sugar and lemon juice in a bowl. Gently stir to coat and let sit for 10 minutes, allowing the berries to release their natural juices and create a syrupy consistency.
04 - Using an electric mixer or whisk, beat heavy cream with powdered sugar and vanilla extract until soft peaks form. Be careful not to over-whip as the cream should remain light and spreadable.
05 - Begin layering by spreading half the custard over the cake base, followed by half the macerated berries and their juices. Add half the whipped cream on top. Repeat the layers with remaining sponge cubes, custard, berries, and whipped cream, ending with a generous layer of whipped cream.
06 - Decorate the top with chocolate eggs, colored sprinkles, and fresh mint leaves if desired. Refrigerate for at least 2 hours to allow flavors to meld and the dessert to set properly before serving.