Combine flour, sugar, lemon zest and salt in food processor. Cut butter into pieces and add to dry mixture. Process until mixture resembles coarse meal. Mix in enough water to form dough. Gather dough and shape into disk.
Whisk together eggs, sugar, cream, lemon juice and lemon zest. Pour filling into crust. Bake at 400 degrees until set, about 25 minutes. Cool completely. Sprinkle top of tart with additional sugar, about 1 Tbls. Cover sides of tart with foil. Broil until sugar caramelizes in spots, about 3 minutes.