Prepare the Whipped Cream:

1. Whip the Cream: In a mixing bowl, combine the heavy cream, powdered sugar, and vanilla extract. Whisk until soft peaks form. Be careful not to overwhip.

Assemble the Trifle:

2. Layer the Cake: Start by placing a layer of cubed sponge cake at the bottom of a large trifle dish or individual serving cups.
3. Add Custard: Spoon a generous layer of vanilla custard over the cake. Spread it evenly to cover the cake cubes completely.
4. Add the Berries: Scatter a handful of mixed berries over the custard layer, ensuring they are spread out evenly.
5. Repeat the Layers: Continue layering cake, custard, and berries until the dish is filled, ending with a layer of custard on top.

Top the Trifle:

6. Finish with Whipped Cream: Spoon a layer of whipped cream on top of the custard layer. Use a spatula to spread it evenly.
7. Garnish: Garnish the whipped cream with more fresh berries, a sprinkle of lemon zest, and a few sprigs of mint for an extra festive touch.

Chill:

8. Chill the Trifle: Cover the trifle and refrigerate for at least 3 hours, or preferably overnight, to allow the flavors to meld and the layers to set.