Gather all your ingredients. You need no cooking for this recipe.
In a medium bowl, combine the mayonnaise, ketchup, yellow mustard, sweet pickle relish, white vinegar, smoked paprika, garlic powder, and onion powder.
Whisk the ingredients together until the sauce is completely smooth and uniform in color.
Taste the sauce. Add a pinch of salt and black pepper as needed.
For the best flavor, cover the bowl and chill the smash burger sauce in the refrigerator for at least 30 minutes before serving. This allows the flavors to meld.
Use generously on your smash burgers or serve as a dipping sauce.
Notes
For a spicier kick, add a dash of cayenne pepper or a few drops of hot sauce.
If you prefer a tangier flavor, substitute the sweet pickle relish with finely minced dill pickles and add 1/2 teaspoon of pickle juice.
This sauce keeps well in an airtight container in the refrigerator for up to one week.