Blend flour and sugar in heavy saucepan. Slowly stir in 1 cup milk until
smooth. Cook and stir over heat until mixture boils and thickens. Stir 1/2 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 extract and butter.
Pour half of mixture into pie shell. Layer strawberries; pour remaining
mixture on top.