Prepare the sponge cake or ladyfingers and allow to cool.
Mix the berries and set aside.
Prepare the vanilla custard according to package instructions.
Whip the heavy cream with powdered sugar and vanilla extract until soft peaks form.
Layer sponge cake or ladyfingers in a large glass bowl.
Pour a layer of vanilla custard over the cake.
Add a layer of mixed berries on top of the custard.
Repeat layers until glass is filled, finishing with whipped cream.
Garnish with additional berries and fresh mint leaves.