Bake and cool pastry shell. Blend flour and sugar in heavy saucepan. Slowly stir in 1 cup milk until smooth. Add rest of milk; cook and stir over direct heat until mixture boils and thickens [be careful of boil-overs!]. Stir half cup of hot mixture into well-beaten egg yolks; stir together. Pour back in saucepan; cook and stir 2 minutes. Remove from heat; stir in vanilla and butter. Pour half of mixture in pie shell. Layer strawberries; pour remaining mixture on top. Cool and serve. Yields 6-8 servings.