Fit the pie crust to a 9 inch tart pan and prick it thoroughly with the tines of a fork. Place the pan in the freezer for 30 minutes to insure that the crust retains its shape during baking. After freezing, bake the tart shell in a 375° F oven for 10 minutes or until golden. Remove the tart shell from the oven and allow it to cool in the pan as you prepare the filling.
For the filling, whisk three eggs with 3/4 cup sugar until well combined. Whisk in the lemon juice, then the cream, followed by the melted butter and lemon zest (if you are using it).
Pour the filling into the prepared tart pan and carefully place in a 375° F oven (this requires concentration and a steady hand as the filling is very liquid). Bake for 25 minutes. Remove from the oven ( the filling should still be a bit wobbly). Cool on a wire rack, then refrigerate until serving time.
Makes 6 to 8 servings.