1. Whip cream, sugar, mascarpone, and lemon zest with a mixer until soft peaks barely form.
2. Lay half of the ladyfingers in a 2-qt. glass serving dish or an 8-in. square pan, separating them a bit if needed for fit. Brush ladyfingers with half of limoncello. Dollop and spread with half of cream mixture, then sprinkle with half of mixed berries. Repeat layers.