Terri Oliver Steffes' Hot Fudge Sauce

4 oz unsweetened chocolate
3 T sweet butter
1/3 c boiling water
1 2/3 c sugar
6 T corn syrup
1 T vanilla

Melt chocolate and butter in heavy saucepan. Carefully add boiling water to milk and stir well. Add sugars and pour into chocolate mixture. Turn heat to medium and stir until mixture starts to boil, then maintain heat just at the boiling point for nine minutes. Remove from heat and cool 15 minutes. Stir in vanilla. Store in refrigerator. Reheat in microwave for 30 seconds in jar.