http://www.seriouseats.com/recipes/2012/08/sauced-creamy-french-dressing-recipe.html
Place ketchup, onion, mayonnaise, vinegar, sugar, Worcestershire sauce, paprika, garlic powder, and salt in jar of a blender. Puree until onion is completely chopped.
With the motor running, slowly pour in vegetable oil. Use immediately or transfer to an airtight container and store in refrigerator for up to two weeks.