Wash and dry all produce. Halve, peel, and slice onion. Melt 1 TBSP butter in a large pan over medium-high heat. Add onion and cook, tossing, until lightly browned, 1-2 minutes. Lower heat to medium and toss in 1 tsp steak spice (we sent more). Season with salt and pepper. Cook, tossing, until very soft and browned, 4-5 minutes.

Heat a drizzle of oil in another large pan over medium-high heat. Pat beef dry with a paper towel, then season all over with salt, pepper, and remaining steak spice. Add to pan and cook, tossing occasionally, until browned and cooked through, 2-4 minutes. Remove from pan and set aside.

Transfer cooked onion to pan used for beef over medium-high heat. Stir in 1 cup of water and stock concentrate, scraping up any browned bits on bottom. Bring to a simmer, then lower heat to medium. Cook until slightly reduced, 2-3 minutes. Remove from heat.

Cut baguettes in half lengthwise. Sprinkle 1/4 of the cheese onto one baguette bottom, then top with half the beef and another 1/4 of the cheese. Remove some onion slices from gravy and arrange on top, then cover with a baguette top to make sandwich. Repeat with remaining baguette and fillings. TIP: It’s OK if you don’t use all the onions.

Wipe out pan used for onions, then melt 1 TBSP butter in it over medium-low heat. Add sandwiches and toast until golden, 1-2 minutes per side. (TIP: Press down on the sandwiches as they toast—try using a heavy pan to keep them flat.)

While sandwiches toast, halve lemon. Toss lettuce in a medium bowl with a large drizzle olive oil and squeeze or two of lemon. Season with salt and pepper. Divide sandwiches and salad between plates. Divide gravy between two small bowls and serve on the side for dipping sandwiches into.