How To make Booneville Butterscotch Pie

3 tablespoons butter -- * see note
2 cups packed brown sugar
2 cups milk
3 eggs
1/4 cup all-purpose flour
1/2 teaspoon salt
1 1/3 teaspoons vanilla extract
1 9 inch pie crust -- baked
3 tablespoons sugar
* Original recipe calls for butter but you can substitute solid margarine if you prefer.
1. Place butter in HEAVY 10-inch skillet. Heat until melted. Add brown
sugar and 1/2 cup milk; mix well. Bring to a boil and cook for 5 minutes, stirring constantly. 2. Beat the egg yolks; stir in remaining milk. Combine flour and salt;
stir egg mixture into this. Add small amount of the hot brown sugar mix gradually. Stir and return this to the mixture in skillet. Cook over low heat, stirring constantly, until thickened. 3. Cool slightly and blend in 1 teaspoon vanilla. Pour into pre-baked and
cooled pie crust. 4. Beat egg whites until stiff peaks form; slowly add sugar and continue
to beat until sugar is dissolved. Fold in the remaining 1/4 teaspoon vanilla. Pile this on top of pie, sealing to edges. Bake in preheated 325-degree oven for about 10-15 minutes or until lightly browned. Serve warm or cold.