Hot Fudge Sauce

from Mom's recipe box

1 square butter
6 oz. semi-sweet chocolate chips
2 c. powdered sugar
1-1/3 c. evaporated milk
1 tsp. vanilla

In medium saucepan, melt butter and chocolate chips. Add evaporated milk to butter/chip mixture. Over head add powdered sugar slowly, boil 8 minutes. Add vanilla.