In a large mixing bowl, beat the heavy cream, powdered sugar, and vanilla extract until stiff peaks form.
In a separate bowl, fold the mascarpone cheese into the lemon curd until smooth.
Gently fold the whipped cream into the lemon curd mixture until well combined.
Spread a thin layer of the lemon cream mixture on the bottom of an 8×8-inch or 9×13-inch dish.
Layer graham crackers over the cream, breaking them to fit as needed.
Spread a generous layer of lemon cream over the graham crackers. Repeat the layers, ending with a layer of lemon cream on top.
Cover the dish with plastic wrap and refrigerate for at least 4 hours, preferably overnight, to allow the layers to set and the flavors to meld.
Before serving, garnish with lemon zest and fresh berries if desired. Slice into squares and serve chilled.
