3 cups brown sugar, loosely packed
3 tablespoons flour
1/2 cup butter or margarine, melted
1 1/2 cups boiling water
2 teaspoons vanilla extract
1/2 cup chopped nuts, if desired

Mix brown sugar and flour together in the top of a double boiler. Add butter or margarine and stir well. Over gently boiling water, cook, stirring occasionally for five minutes.

Slowly add boiling water to the sugar mixture while continuing to stir constantly. Continue to cook and stir until sauce is thickened. Remove from heat and stir in vanilla extract. Stir in nuts, if desired.