A tangy and flavorful sauce perfect for enhancing your burgers.
In a small bowl, combine the ketchup and mustard.
Use a whisk for a smoother blend.
Add the finely chopped onion and fresh parsley to the bowl.
Ensure the onion is finely chopped to blend well with the sauce.
Stir all the ingredients together until well combined.
Let the sauce sit for a few minutes to allow the flavors to meld.
Serve the sauce as a topping for burgers or as a dip for fries.
Refrigerate any leftovers in an airtight container.