Combine 2/3 cup sugar, flour and salt in a 2qt. saucepan. Gradually stir in milk until smooth. Cook over medium heat, stirring constantly, until thickened and mixture comes to a boil. Boil and stir 1 minute. Remove from heat and stir a small amount of hot mixture into egg yokes; return all to saucepan. Cook over low heat until thickened, about 2 minutes. Do not boil. Remove from heat and stir in vanilla. Gently fold in sour cream, small amount at a time. Cover and cool to lukewarm, meanwhile, line bottom of pie shell with strawberries. Spoon the filling over the strawberries. Preheat oven to 350 ?F. Beat egg whites and cream of tartar until frothy. Gradually add 1/2 cup sugar and continue beating until stiff peaks form. Spread meringue over filling, making sure that meringue covers filling completely and is sealed to crust. Bake until lightly browned, about 5 minutes. Remove from oven and chill 3 to 4 hours before serving.