Add mayonnaise, relish, mustard, vinegar, garlic powder, onion flakes, paprika, and white pepper to a bowl. Stir to combine. Use at once or store in the refrigerator for up to a week.
Notes
Most people assume the reddish tint comes from ketchup, but it's actually paprika that gives it that warm color! If you add ketchup, it will throw off the whole flavor of the sauce.
Store homemade Big Mac sauce in an airtight container in the fridge for up to a week.
This sauce is pretty thick! If you want to thin it out, you can mix in a small amount of water until it reaches the desired consistency.