Mom's Lemon Custard Pie

Preheat oven to 325°. On a lightly floured surface, roll dough to a 1/8-in.-thick circle; transfer to a 9-in. pie plate. Trim crust to 1/2 in. beyond rim of plate; flute edge. Refrigerate while preparing filling., In a large bowl, beat sugar and butter until well blended. Add egg yolks, one at a time, beating well after each addition. Add milk, flour and salt; mix well. Stir in lemon juice and zest; set aside. In a small bowl, beat egg whites until stiff peaks form; gently fold into lemon mixture., Pour into crust. Bake until lightly browned and a knife inserted in the center comes out clean, about 1 hour. Cool on a wire rack. If desired, garnish with whipped cream, lemon and mint. Store in the refrigerator.