Preheat the oven to 400 degrees F (200 degrees C). In a saucepan, combine flour and sugar. Stir in milk, butter, salt, and vanilla. Cook, stirring constantly, until the mixture comes to a boil. Pour into an unbaked pie shell. Bake at 400 degrees F (200 degrees C) for 5 minutes. Reduce heat to 350 degrees F (175 degrees C) and continue baking for 25 minutes.
Preheat the oven to 400 degrees F (200 degrees C). In a saucepan, combine flour and sugar. Stir in milk, butter, salt, and vanilla. Cook, stirring constantly, until the mixture comes to a boil. Pour into an unbaked pie shell. Bake at 400 degrees F (200 degrees C) for 5 minutes. Reduce heat to 350 degrees F (175 degrees C) and continue baking for 25 minutes.