Peel and grate yellow onion on a box grater until you have 1 tbsp grated onion, including any juices; transfer the grated onion and its juices to a small bowl.

Add the remaining ingredients to the bowl: ½ cup mayo (good quality), 2 tbsp sweet pickle relish, 2 tsp yellow mustard, ½ tsp white vinegar, ½ tsp sweet (not smoked) paprika, ½ tsp onion powder, ¼ tsp garlic powder, and ¼ tsp salt.

Whisk everything vigorously until smooth and evenly combined, scraping the sides and bottom of the bowl.

Transfer the sauce to an airtight container and refrigerate. Store in the fridge for up to 7 days.