Sarah's Butterscotch Pie

An Old Indiana Recipe:

2 ½ cups milk
2 eggs separated
¼ cup flour
1 cup dark brown sugar, firmly packed
½ cup water
1/8 tsp. salt
1 ½ Tbsp. butter or margarine
1 tsp. vanilla
1 8-inch baked pastry shell

Thoroughly combine ½ cup milk, egg yolks and flour. Set aside. Scald remaining 2 cups of milk over hot water. Combine brown sugar, water and salt in skillet. Place over low heat and bring to a gentle boil. Cook until mixture thickens and a few bubbles break sending up not whiffs, but puffs of smoke. Add caramelized sugar very slowly, stirring constantly, to scalded milk. When smooth, gradually stir in egg-yolk mixture and cook, stirring constantly, over hot water until thick. Remove and add butter or margarine and vanilla. When fat has melted, stir it in. Cool. Pour filling into cooled pie shell. Make a meringue using the egg whites, ¼ tsp. Cream of tartar and ¼ cup sugar. Spread over pie. Bake in hot oven (400 degrees) for 8 to 10 minutes or until delicately browned.