Blend the ingredients: Put the mayonnaise, ketchup, yellow mustard, pickle slices, garlic powder, paprika, cayenne pepper (if using), pickle juice, and sugar into a blender or food processor.
Puree until smooth: Blend the mixture until it's fully combined and smooth. There shouldn't be any chunks or large pieces of pickle.
Taste and adjust: Give the sauce a taste and adjust the seasonings as needed. If you want it a bit sweeter, add a bit more sugar. If it needs more tang, add a bit more pickle juice or mustard.
Refrigerate: Once you're happy with the flavor, transfer the sauce to a container with a lid and refrigerate it for at least an hour before using. This allows the flavors to meld together.
Serve: Use this sauce just like you would the original ShackSauce. It's great on burgers, fries, hot dogs, and more!