Heat the vegetable oil in a medium pot over medium heat. Add the onions and garlic and cook, until the onions are golden, 6 to 7 minutes. Stir in the ketchup, 1 cup water, the vinegar, brown sugar, steak sauce, Worcestershire sauce, molasses, mustard, celery seed and 1 teaspoon salt. Bring to a boil, then reduce the heat to medium-low and simmer until the onions are tender, about 15 minutes. Stir in the liquid smoke, if using. Strain the sauce, pressing on the solids to extract any liquid.