01 - Combine frozen mixed berries, granulated sugar, and lemon juice in a saucepan. Cook over medium heat for 5 to 7 minutes until berries are soft and juicy, stirring occasionally. Remove from heat and allow to cool.
02 - Heat whole milk in a medium saucepan until steaming, avoiding boiling. In a separate bowl, whisk egg yolks, sugar, and cornstarch until smooth. Gradually whisk hot milk into the egg mixture. Return to saucepan and cook over low heat, stirring constantly, until thickened, about 3 to 5 minutes. Remove from heat, stir in vanilla extract, and cool completely.
03 - Place half of the ladyfingers or pound cake slices in the base of a trifle dish or glass bowl. Drizzle with half of the berry liqueur or orange juice. Spread half of the cooled berry mixture over the cake layer, then layer with half of the custard. Repeat with remaining cake, liqueur, berries, and custard.
04 - Beat heavy cream, powdered sugar, and vanilla extract with an electric mixer or whisk until soft peaks form.
05 - Spread whipped cream over the top custard layer. Garnish with fresh berries, grated chocolate or almonds, and mint leaves as desired.
06 - Refrigerate for at least 2 hours or overnight before serving to enhance flavor and texture.