01 - Combine frozen berries, sugar, and lemon juice in a saucepan. Cook over medium heat for 5 to 7 minutes, stirring occasionally, until softened and juicy. Remove from heat and let cool.
02 - Heat milk in a saucepan until steaming but not boiling. In a 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, approximately 3 to 5 minutes. Remove from heat, stir in vanilla extract, and cool completely.
03 - Place half the ladyfingers or pound cake slices in a trifle dish or glass bowl. Drizzle with half the berry liqueur or orange juice. Spread half the cooled berry mixture over the cake, then top with half the custard. Repeat layering with remaining cake, liqueur, berries, and custard.
04 - Beat heavy cream, powdered sugar, and vanilla extract in a large bowl until soft peaks form.
05 - Spread whipped cream over the top custard layer. Garnish with fresh berries, grated chocolate or almonds, and mint leaves if desired. Chill for at least 2 hours or overnight before serving to develop flavors and texture.