In a blender or food processor, combine 1 can (8 oz.) tomato sauce, 3 tablespoons firmly packed brown sugar, 2 tablespoons chopped garlic, 1 teaspoon chopped fresh serrano chili, 1/4 cup vinegar, 1 1/4 cups golden raisins, and 1/3 cup water; whirl until raisins are coarsely chopped.
Pour into a 10- to 12-inch frying pan. Stir sauce over high heat until reduced to 1 1/2 cups, about 10 minutes.
Serve warm, at room temperature, or cold, adding salt to taste.