Heat the large deep skillet over medium-high heat. Add the ground beef and cook, breaking it into crumbles, until browned and cooked through, 5–6 minutes. Drain off any excess fat if needed, leaving about a tablespoon for flavor.

Add the onion to the beef and cook 2–3 minutes, until softened. Stir in the garlic, salt, pepper, paprika, and onion powder and cook 1 minute, until fragrant. Add the tomato paste, ketchup, and mustard; stir and cook 1–2 minutes, until the paste darkens slightly and coats the beef.

Pour in the beef broth, scraping up any browned bits from the bottom of the pan. Stir in the dry shell pasta and bring to a boil over high heat.

Reduce the heat to medium-low, cover, and simmer 12–14 minutes, stirring once or twice, until the pasta is al dente and has absorbed most of the broth. The shells finish plump and coated in a beefy, tomatoey sauce.

Remove from the heat. Stir in the milk, then add the cheddar a handful at a time, stirring until melted and silky before adding more. Stir in the diced pickles. Let stand 2 minutes — the sauce thickens as it rests.

Spoon into bowls and top with shredded lettuce, extra pickles, and a drizzle of ketchup and mustard. Serve immediately, while the cheese is at maximum melt.