Cheesy French Onion Hamburger (Print version)

Juicy beef patties topped with jammy caramelized onions and melted Gruyère on a toasted brioche bun, inspired by the bold flavors of French onion soup.

# Ingredients:

For the caramelized onions

01 - 2 large yellow onions (about 1 lb / 450 g total), thinly sliced
02 - 2 tablespoons unsalted butter
03 - 1 tablespoon olive oil
04 - 1/2 teaspoon salt
05 - 1/4 cup (60 ml) beef broth
06 - 1 tablespoon Worcestershire sauce
07 - 1 teaspoon fresh thyme leaves (or 1/2 tsp dried)

For the patties

08 - 1.5 lbs (680 g) ground beef, 80/20
09 - 1 tablespoon Worcestershire sauce
10 - 1 teaspoon garlic powder
11 - 1 teaspoon onion powder
12 - Salt and black pepper
13 - 1 tablespoon neutral oil

For assembly

14 - 4 slices Gruyère cheese (about 3 oz / 85 g total)
15 - 4 brioche hamburger buns, split
16 - Dijon mustard (optional)
17 - Fresh thyme sprigs for garnish

# Instructions:

01 - Melt the butter with the olive oil in a wide skillet over medium-low heat. Add the sliced onions and salt. Cook, stirring every 5 to 8 minutes, for 40 to 45 minutes until deeply golden, very soft, and reduced to about a third of their original volume. Do not raise the heat to speed this up.
02 - Add the beef broth, Worcestershire sauce, and thyme to the pan. Stir and cook for 2 to 3 minutes, scraping up any browned bits from the bottom, until most of the liquid has absorbed and the onions look glossy. Remove from heat and keep warm.
03 - Divide the ground beef into 4 equal portions (about 6 oz / 170 g each). Add the Worcestershire sauce, garlic powder, and onion powder and fold gently until just combined. Shape each portion into a patty about 3/4 inch thick, pressing a shallow indent in the center with your thumb. Season both sides generously with salt and pepper.
04 - Heat a cast-iron skillet over medium-high heat until very hot. Add a thin film of oil. Cook the patties for 3 to 4 minutes without moving them, then flip once and cook for 2 to 3 minutes more for medium. The USDA recommends an internal temperature of 160°F (71°C) for ground beef. Work in batches if the pan is crowded.
05 - In the final minute of cooking, lay one slice of Gruyère over each patty. Add 1 tablespoon of water to the pan and cover with a lid immediately. The steam will melt the cheese completely in about 60 seconds.
06 - Toast the buns cut-side down in a dry skillet for 1 to 2 minutes until lightly golden. Spread Dijon mustard on the bottom bun if using. Set a cheesy patty on each bun, spoon a generous portion of warm caramelized onions on top, garnish with a thyme sprig, and close with the top bun. Serve right away.

# Good to know:

01 - The caramelized onions can be made up to 5 days ahead and refrigerated.
02 - Best served immediately after assembly so the brioche bun stays crisp.
03 - Cook ground beef to 160°F (71°C) internal temperature per USDA guidance.

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