Mix molasses, catsup, 1/2 cup brown sugar, liquid smoke, onion salt, vinegar, mustard and garlic powder. Simmer for 20 minutes. Taste, add additional 1/4 brown sugar, if desired, and cook another 5 minutes. Mix 1-1/2 teaspoons corn starch with 1 tablespoon water. Stir to mix well. Pour into hot mixture and cook until slightly thickened, about 5 minutes. Cool.