• Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce. • Cut potatoes into 1/2-inch-thick wedges. • Toss potatoes on a baking sheet with a large drizzle of oil, salt, and pepper. Roast on top rack until browned and tender, 20-25 minutes.

• Open and drain tuna, squeezing out any excess liquid. Halve, peel, and finely dice half the onion (all for 4 servings). Zest and quarter lemon.

• In a large bowl, combine tuna, diced onion, half the mayonnaise (you’ll use the rest later), 1/4 tsp celery salt (you’ll use the rest later), a squeeze of lemon juice, and pepper (1/2 tsp celery salt and a big squeeze of lemon juice for 4 servings). Taste and season with salt if necessary.

• Place bread on a clean work surface. Place gouda on half the bread slices. Spread with tuna mixture. Top with Monterey Jack and remaining bread slices to form sandwiches. • Heat 2 TBSP butter and a drizzle of oil in a large pan over medium heat. Carefully add sandwiches; cook, gently pressing with a spatula or heavy-bottomed pan, until cheese melts and bread is golden, 2-4 minutes per side, adding 1 TBSP butter when flipping. TIP: Lower heat if sandwiches begin to brown too quickly. (For 4 servings, work in batches; wipe out pan between batches and add more butter and oil as needed.) • Transfer to a cutting board.

• In a small bowl, combine ketchup and remaining mayonnaise. Set aside. • When potatoes are done, add to a second large bowl. Toss with a squeeze of lemon juice (big squeeze of lemon juice for 4 servings), lemon zest to taste, and remaining celery salt to taste. Season with pepper.

• Halve tuna melts on a diagonal; divide between plates. Serve with potato wedges and special sauce on the side for dipping.