Thoroughly mix crust ingredients and pack into a nine inch pie pan. Bake at 190ºC or 10 minutes and put aside to cool. Reduce oven temperature to 325 degrees. In a mixing bowl, combine condensed milk, lemon juice, lemon zest and egg yolks. Stir until mixture thickens. Pour into cooled crust. Add cream of tartar to the egg whites and beat until almost stiff. Add sugar gradually, beating until stiff and glossy but not dry. Pile lightly on pie filling. Bake at 325 until lightly browned, about 15 minutes. Cool thoroughly. Enjoy! Hint: try to get the crust thickness very even and not too thick.