Preheat oven to 425 degrees. Separate the eggs. Beat the egg yolks and set the whites aside. Combine the 1 cup white sugar, flour, cornstarch and salt in a saucepan. Gradually stir in the water. Cook over medium heat until thickened. Very, very important, do not undercook! Gradually stir the cooked sugar mixture into the beaten egg yolks, beating constantly. Return the mixture to low heat and cook, stirring constantly, for 2 minutes. Stir in the butter, lime juice and lime zest. Let mixture cool slightly.
Beat egg whites until light and frothy. Add the cream of tartar and continue beating until stiff peaks form. Gradually beat in the remaining 6 tablespoons white sugar and beat until the meringue is stiff and glossy.
Pour the lime filling into the prepared pie shell. Then pile the meringue on top, spreading it until it touches the edges of the pastry to prevent the meringue from shrinking. Bake pie at 425 degrees for 5 to 6 minutes or until meringue top is golden brown.