Adjust rack to top position and preheat oven to 450 degrees. Wash and dry all produce. Quarter pickle lengthwise. Halve, peel, and thinly slice onion.

Cut potatoes into 1/2-inch-thick wedges. Toss on a baking sheet with a drizzle of oil, Fry Seasoning, salt, and pepper. Roast on top rack, flipping halfway through, until golden brown and tender, 20-25 minutes.

Meanwhile, heat a drizzle of oil in a large pan over medium heat. Add onion and cook, stirring occasionally, until browned and softened, 8-10 minutes. (TIP: If onion begins to brown too quickly, add a splash of water.) Stir in vinegar and 1 tsp sugar (2 tsp for 4 servings). Continue cooking until caramelized and jammy, 2-3 minutes more. Season with salt and pepper. Turn off heat; transfer to a small bowl. Wash out pan.

Mince or grate 1 clove garlic (2 cloves for 4 servings). In a second small bowl, combine mayonnaise, sour cream, mustard, and minced garlic to taste. Season with salt and pepper. Halve buns; toast until golden.

Season patties all over with salt and pepper. Heat a drizzle of oil in pan used for onion over medium-high heat. Add patties and cook until browned, 3-5 minutes per side. Top each patty with gouda. Reduce heat to medium; cover pan until cheese is melted, 1-2 minutes.

Spread bottom buns with half the ketchup and top buns with a thin layer of aioli. Fill buns with patties and as much onion jam as you like. Serve with potato wedges, pickle spears, and remaining aioli and ketchup on the side.