01 - Combine strawberries, blueberries, raspberries, and optional sugar in a medium bowl. Toss gently and let stand for 10 minutes to allow juices to release.
02 - In a large mixing bowl, whip the heavy cream to soft peaks. Add mascarpone or cream cheese, sugar, and vanilla extract. Whip until mixture is smooth, thick, and thoroughly combined.
03 - If making vanilla custard from scratch, prepare and cool completely before assembling.
04 - Arrange half the cubed cake evenly on the bottom of a trifle bowl or individual glasses.
05 - Spoon half of the macerated berries and their juices over the cake layer.
06 - Spread half of the vanilla custard over the berries, then follow with half of the vanilla cream mixture.
07 - Repeat the layering with remaining cake, berries, custard, and vanilla cream.
08 - Top with extra berries and fresh mint leaves, if desired.
09 - Refrigerate assembled dessert for at least 1 hour before serving to allow flavors to meld.