1/2 c. (1 stick) butter
4 (1 oz.) sq. Baker's unsweetened chocolate
3 c. sugar
1 (14 1/2 oz.) can evaporated milk
1/2 tsp. salt
1 tsp. vanilla

Melt butter and chocolate in top of double boiler, stir to blend. Add milk, sugar, salt and mix well. Cook on simmer for 20 minutes, stirring occasionally, then add the vanilla.