Butterscotch Pie

2 egg yolks
1 tablespoons butter
1 cup brown sugar
2 tablespoons flour
1 1/2 cups milk
1 teaspoon vanilla
1 8 ince pie shell

Cream together the egg yolks, butter, sugar and flour. Add milk and mix. Slowly cook until thick. Add vanilla and pour into pie shell. Top with whipped cream and serve.