In a medium bowl, combine the flour, salt, sugar, and lemon zest. Cut the butter into the dry ingredients until the mixture resembles coarse crumbs. In a small bowl, combine the egg, the yolk, the liqueur and confectioners' sugar, and stir this mixture into the flour mixture with a fork until it just comes together. Turn the mixture onto a floured board and gently work the mixture until a dough is formed. Press the dough into a disc shape about 6 inches across, wrap tightly in plastic wrap and freeze for 15 minutes. Remove from the freezer and quickly roll the dough so that it fills out a buttered, 12 to 14-inch tart pan. Place the dough in the pan, trimming the edges, wrap the pan in plastic wrap and refrigerate for 30 minutes.
Preheat the oven to 400 degrees F.
Remove the pastry from the refrigerator and prick it all over with a fork. Bake for 10 minutes, reduce heat to 375 degrees F and continue to bake for 10 to 15 minutes more, until golden. Remove from oven and allow to cool. Using baking beads will help set the shell and eliminate shrinkage.
To make the filling, in a medium bowl, combine the orange juice, zest, sugar, and mascarpone and beat well. Add the eggs 1 at a time and continue to beat. When all eggs have been added, beat in the liqueur.
Pour the filling into the cooled pastry shell and bake at 350 degrees F for 40 to 50 minutes, until the custard is set. Allow to cool dust with confectioners' sugar.