Place the two entire cans of chiles (and their canning sauce) in a blender along with the molasses, vinegar, sugar and ½ cup water. Process until completely smooth. Scrape into a small 2-quart) saucepan set over medium heat. Let the mixture come to a boil, then turn the heat to medium-low and continue simmering, stirring regularly, until the mixture is the consistency of tomato paste, about 30 minutes. Remove from the heat and stir in the soy sauce. If necessary, add some water, a little at a time, until the salsa is the consistency of runny ketchup. Cool, taste and season with salt—it may not need any, depending on the saltiness of your soy sauce but keep in mind that Salsa Negra should be seasoned highly, both to preserve it for longer storage and to make it useful as a seasoning. Transfer the salsa to a pint-size jar and store, covered, in the refrigerator, where it will last for a month or two.