Mistral - I found this recipe today. It says that it keeps for ever in the fridge, so possibly it would take a boiling water bath for preservation. Unfortunately I don't know enough about canning to offer any advice on that.
From "Viva Tradiciones - South Texas Cooks from Brush to Bay" Corpus Christi, Texas Junior League ISBN: 0-9609144-2-0
Hot Fudge Sauce:
1 (14 oz.) can sweetened condensed milk
1 cup water
1/8 tsp. salt
1/2 cup sugar
1 (8 oz.) package semi-sweet chocolate chips
Combine all ingredients in top of a double boiler. Cook over boiling water until thick, stirring frequently, approximately 15 minutes.
Keeps indefinitely in refrigerator. Reheat in top of double boiler.
Yield: 2 cups