1.Preheat oven to 375 degrees. Place the 4 sheets of graham crackers into a food processor until crumbs form. Pour crumbs into a small bowl with a pinch of salt and stir in melted butter.
2.Divide crumbs into two small tart tins and press down with the back of a spoon. Place crust in the oven and bake for 5 minutes. Take crust out to cool and set aside.
3.Meanwhile, in a large bowl, mix together the cream cheese, sugar, lemon juice and lemon zest. Set aside.
4.Pour the heavy cream into the bowl of an electric mixer with a whisk attachment. Whip until stiff peaks form, about 4 minutes.
5.Fold the whipped cream into the cream cheese mixture. Spoon over the cooled crust and refrigerate for at least 20 minutes. Unmold the tart and serve immediately.