Hot Fudge Sauce - Microwave

In a microwave proof bowl, combine margarine, water and cocoa.
With wire whisk, blend in condensed milk.
Microwave on high 1 minute then whisk to blend.
Microwave 1 1/2 minutes more on high. Add vanilla and blend with whisk completely.
Serve over your favorite ice cream.
Store in 1 pint canning jar, cool and refrigerate.
Can be rewarmed in jar (lid removed) in microwave--add a bit of water if it thickens too much.