1. Toss berries with 1/4 cup sugar and let macerate for 15 minutes.
2. In a medium saucepan, whisk together milk, 1/2 cup cream, 1/3 cup sugar, egg yolks, and cornstarch. Cook over medium heat, stirring constantly, until thickened (about 5-7 minutes). Remove from heat, stir in 1 tsp vanilla, and let cool slightly.
3. In a large bowl, whip 1 1/2 cups cold cream with powdered sugar and 1/2 tsp vanilla until soft peaks form.
4. Arrange half the cake cubes in the bottom of a trifle dish. Drizzle with half the fruit juice. Top with half the macerated berries. Pour half the custard over the berries. Spread half the whipped cream on top.
5. Repeat layers with remaining cake, juice, berries, custard, and whipped cream.
6. Cover and refrigerate for at least 2 hours or overnight. Garnish with mint and extra berries before serving.
Tips
For a non-alcoholic version, use fruit juice instead of sherry.
Trifle can be made a day ahead; the flavors meld beautifully.