Prepare the hot fudge: Combine chocolate and margarine in a double boiler set over a pan of simmering water, or melt in the microwave in 30-second increments. Stir until smooth.
Stir in water, cocoa, sugar, and corn syrup. Divide into containers, label and freeze.
Recipe by Between Carpools at https://betweencarpools.com/another-5-things-that-renee-tries-to-always-have-in-her-freezer/