Make the ShackSauce: Stir together 0.5 cups mayonnaise(for ShackSauce), 1 tablespoons ketchup, 1 tablespoons ketchup1 tablespoons yellow mustard, 1 teaspoons pickle brine, and 1 pinch cayenne(for ShackSauce). Refrigerate for at least 15 minutes before serving.
Cut the potatoes: Scrub 2 pounds russet potatoes (about 4 medium) clean. Using a crinkle cutter knife, slice into fries about ¼ to ⅓ inch thick. Keep them uniform so they cook evenly.
Soak in cold water: Place the cut fries in a large bowl of cold water and soak for at least 20–30 minutes, (up to 2 hours). This removes excess starch for crispier fries. Don't skip this step.
Dry and season: Drain and pat the fries completely dry with paper towels. Toss with 2 tablespoons olive oil or avocado oil, 1 teaspoons kosher salt, 0.5 teaspoons black pepper 0.5 teaspoons garlic powder, and 0.5 teaspoons smoked paprika until every fry is evenly coated.
Air fry: Air fry at 380°F in a single layer, working in batches if needed. Cook for 18–20 minutes, shaking the basket every 6–7 minutes, until the ridges are deep golden brown and crispy. (Oven method: bake at 425°F on a wire rack for 25–30 minutes, flipping once.)
Season and serve: While the fries are hot, immediately toss with the seasoning salt: 1 teaspoons kosher salt (seasoning salt), 0.3 teaspoons celery salt, 0.3 teaspoons garlic powder (seasoning salt), 0.3 teaspoons onion powder and 1 pinch cayenne pepper Serve right away with ShackSauce or your dipping sauce of choice.