Mix the sauce. It should be well blended and smooth in appearance.
Keep in the fridge to cool for later (with a lid or cling film over the container), or use it straightaway on your burger.
Video
Notes
Instead of freshly chopped onion, use onion powder. For every tablespoon of freshly chopped onion, use about ½ teaspoon onion powder at most. Onion powder is more intense in flavor than freshly chopped onion.
Use an original store bought Mayonnaise, Ketchup, and Dijon Mustard.
Make the big mac burger sauce vegan by substituting the Mayonnaise with vegan eggless mayonnaise.
Make a bigger batch and store your favorite Big Mac Sauce in the fridge!
Don't limit yourself. Try the big mac sauce on other burger varieties such as chicken or even wild game meat.