Prepare the sponge cake or ladyfingers, allowing them to cool completely.
Slice the sponge cake into even pieces for layering.
Lightly soak the sponge cake pieces in sherry or fruit juice if using.
Add a layer of sponge cake at the bottom of a large glass bowl or trifle dish.
Top the cake layer with mixed berries.
Pour a layer of custard over the berries.
Add a layer of whipped cream on top of the custard.
Repeat layering until the dish is filled, ending with whipped cream.
Garnish the top with more berries and mint leaves.
Refrigerate for at least 2 hours before serving.