Adjust racks to top and middle positions and preheat oven to 425 degrees. Wash and dry produce. 

Cut potatoes into ½-inch-thick wedges. Halve, peel, and thinly slice onion. Cut each cheddar slice into 6 small squares (you'll have 12 squares total; 24 squares for 4 servings). Trim and discard root end from lettuce; dry leaves thoroughly, then chop into bite-size pieces.

Toss potatoes on a baking sheet with a drizzle of oil, Fry Seasoning, salt, and pepper.

Roast on top rack, tossing halfway through, until crisp and tender, 20-25 minutes.

Heat a large drizzle of oil in a large, preferably nonstick, pan over medium-high heat. Add onion; cook, stirring occasionally, until browned and softened, 8-10 minutes. TIP: Lower heat and add a splash of water if onion begins to brown too quickly.

Add 2 TBSP water, 1 tsp Worcestershire sauce (you'll use more later), and 1 tsp sugar to pan with onion (use 4 TBSP water, 2 tsp Worcestershire sauce, and 2 tsp sugar for 4 servings); cook, stirring, until caramelized, 2-3 minutes.

Season with salt and pepper. Turn off heat; transfer to a small bowl. Wipe out pan.

In a large bowl, combine beef*, 1 tsp Worcestershire sauce (2 tsp for 4 servings), salt, and pepper. (Be sure to measure the Worcestershire—we sent more!)

Form mixture into 6 ½-inch-thick patties (12 patties for 4).

Heat a drizzle of oil in pan used for onion over medium-high heat. Add patties; cook to desired doneness, 2-3 minutes per side. TIP: Carefully drain any excess grease from pan if needed.

Turn off heat; top each patty with two squares of cheddar. Cover pan until cheese melts, 1-2 minutes. 

While cheese melts, place buns directly on middle oven rack; toast until warmed through, 2-3 minutes. 

In a medium bowl, toss together lettuce, dressing, and Parmesan. Season with salt and pepper.

Once buns are toasted, gently separate tops from bottoms. Fill buns with caramelized onion and patties.

Divide sliders, salad, and oven fries between plates. Serve with ketchup and smoky mustard on the side.