Onion Salad Dressing 2 Ingredients: 1/2 cup of finely chopped onion. 1/4 cup of cider vinegar. 1/4 cup of sugar. 1/2 teaspoon of salt. 1/2 teaspoon of dry mustard. 1/4 teaspoon of celery seed. 1/2 cup of oil. Directions: Combine all of the ingredients, except oil, in blender, mix well, stopping as necessary to scrape down sides of container. With blender running, gradually pour in oil, blending until dressing is creamy. Transfer to container with tight fitting lid and refrigerate before using. Whisk or shake, if dressing separates on standing. Makes 1 cup. Download This Recipe