French Onion Skillet Smashed Burgers with Melted Gruyère Tips, FAQ & printable recipe

Tips for success

For the best crust, make sure the skillet is smoking hot before adding the beef. Use a heavy spatula and press down firmly to flatten the patty in one motion.

Do not move the patty until it releases easily from the pan—this ensures a crispy, caramelized edge.

To caramelize onions faster, add a pinch of salt at the beginning to draw out moisture.

If they start to stick, add a tablespoon of water or broth to deglaze the pan. The onions are done when they are deep brown and sweet, not just translucent.

Variations

• Beef and Mushroom: Add sautéed mushrooms to the onions for an earthy twist. Cook 8 oz sliced mushrooms with the onions during the last 10 minutes of caramelizing.
• Spicy Kick: Mix 1 tsp smoked paprika or a pinch of cayenne into the Dijon aioli for a smoky heat. Or add pickled jalapeños on top.
• Turkey Burger: Swap ground beef for ground turkey (93/7). Since turkey is leaner, add 1 tbsp olive oil to the meat and cook to 165°F (74°C).
• Veggie Version: Use plant-based burger patties and vegan cheese. Caramelize onions as directed and use vegan aioli. Cook patties according to package instructions.

Storage and make-ahead

Fridge

Store leftover burgers in an airtight container in the refrigerator for up to 3 days. Reheat in a skillet or oven to restore crispiness.

Freezer

Freeze cooked burgers (without buns) for up to 2 months. Wrap individually in plastic wrap and place in a freezer bag.

Reheat

Reheat patties in a skillet over medium heat for 2–3 minutes per side, or in a 350°F (175°C) oven for 5–7 minutes. Toast buns separately.

Leftover burgers can be stored in an airtight container in the refrigerator for up to 3 days.

Reheat in a skillet over medium heat until warmed through, or in the oven at 350°F (175°C) for 5–7 minutes. The buns may soften, so toast them again if desired.

The caramelized onions can be made up to 3 days ahead and stored in the refrigerator. The beef balls can be formed and refrigerated for up to 24 hours. Assemble the burgers just before cooking for the best texture.

Serving ideas

Serve the burgers immediately after assembling, while the cheese is still molten and the patties are crispy.

Pair with a side of crispy fries, a simple green salad, or pickles to cut through the richness. A cold beer or sparkling water complements the savory flavors.

For a more indulgent meal, serve the burgers with a small bowl of French onion soup for dipping, or add a handful of arugula for a peppery contrast. The Dijon aioli can be served on the side for extra tang.

Frequently asked questions

Recipe card

French Onion Skillet Smashed Burgers with Melted Gruyère

Prep 15 minCook 35 minTotal 50 minServes 2

Ingredients

• 2 large yellow onions, thinly sliced
• 2 tbsp unsalted butter
• 1/4 cup beef broth
• 1 lb ground beef (80/20)
• kosher salt, to taste
• freshly ground black pepper, to taste
• 4 oz Gruyère cheese, sliced
• 2 brioche burger buns, split
• 1/4 cup Dijon aioli

Instructions

1. Melt the butter in a large cast-iron skillet over medium-low heat. Add the sliced onions and cook slowly, stirring occasionally, for 25–30 minutes until they are deep golden brown and jammy. Add the beef broth and continue cooking for 2–3 minutes, scraping up any browned bits. Season with salt and pepper to taste. Transfer the onions to a bowl and wipe the skillet clean.
2. Divide the ground beef into 4 equal portions (about 4 oz each). Shape each portion into a loose ball without overworking the meat. Keep the balls chilled until ready to cook.
3. Heat the same cast-iron skillet over high heat until it is smoking hot. Place one beef ball in the skillet and immediately smash it down with a spatula until it is very thin, about 1/4 inch thick. Season generously with salt and pepper. Cook for 2–3 minutes without moving until the edges are browned and crispy.
4. Flip the patties and immediately pile a generous amount of caramelized onions on top of each patty. Lay slices of Gruyère cheese over the onions. Cover the skillet with a lid or dome and cook for 1–2 minutes until the cheese is melted and bubbly.
5. While the patties finish, toast the brioche buns cut-side down in a dry skillet or under a broiler until golden brown.
6. Spread the Dijon aioli on the bottom half of each toasted bun. Place one cheesy patty on each bottom bun, then top with the second patty (if using double) or additional onions. Close with the top bun and press down gently.

Contains: gluten, milk, eggs, mustard

Estimated nutrition per serving

Calories

780

Protein

45 g

Carbohydrates

40 g

Fat

48 g

Automatic estimate from the ingredient list, not laboratory-verified.