Cream the butter and sugar; add the egg
yolks, beating after each addition. Beat in flour and buttermilk; add
the lemon juice, lemon peel, nutmeg, and a pinch of salt. Beat the egg
whites until stiff; fold into the filling. Pour the filling into the pie
shell; cook in center of a preheated 325° oven until the custard is set
and slightly brown, about 1 hour. Serve with berries, fresh fruit, or
dessert sauce.