1/2 cup vegetable oil
1/4 cup vinegar
1/4 cup vinegar-base with bouillon granules
1/4 teaspoon salt
1/4 teaspoon ground black pepper
1/4 teaspoon dry mustard
In a small bowl, mix the oil, vinegar, vinegar-base, salt, pepper, mustard (if desired), and onions.
Cover and refrigerate at least 2 hours before serving.