If using store-bought sponge or pound cake, cut it into small cubes (about 1-inch pieces). If using homemade cake, slice it into layers and cut it into similar-sized cubes. Optionally, drizzle the cake cubes with a little bit of sherry or fruit juice for added moisture.

1. In a mixing bowl, whip the heavy cream, powdered sugar, and vanilla extract together until stiff peaks form.
2. In individual glass cups or jars, layer the ingredients starting with a layer of cake cubes at the bottom. Add a layer of custard over the cake, followed by a layer of whipped cream. Add a few spoonfuls of mixed berries, then repeat the layers until you reach the top of the cup.
3. Top each trifle with additional whipped cream, a few more berries, and a drizzle of fruit preserves or jam, if desired.
4. Refrigerate the trifles for at least 2 hours to allow the flavors to meld together and the dessert to firm up. Serve chilled.