1 store-bought sponge cake tart shell, 12-inch diameter, available in produce or bakery departments
2 ounces chilled limoncello liqueur
1 cup heavy cream
1 cup mascarpone cheese
1/3 cup lemon curd
1/2 pint raspberries
1/2 pint blackberries
2 teaspoons lemon zest
2 tablespoons very thinly sliced mint leaves