Hot Fudge Sauce

In double boiler, melt unsweetened chocolate with butter. Stir to combine, then add the boiling water. Stir well until combined, then add the sugar and corn syrup.

Bring sauce to a gentle boil over direct heat. Do not allow to boil furiously. Do not stir. For ordinary sauce, boil 3 minutes, covered to wash down any crystals that form. Uncover, reduce heat, and cook 2 more minutes.

For a sauce that will harden, boil uncovered 3 minutes more. Just before serving, add vanilla or rum.