Burgers with caramelized onions

Ingredients:

• 2 tablespoons extra-virgin olive oil
• 1 large onion, sliced ​​into thin half rings
• 0.5 tsp sugar
• 0.5 cups lightly salted chicken broth
• 2 tbsp + 1 tsp Worcestershire sauce
• 700 g of ground beef
• 1 tsp onion powder
• 4 hamburger buns, cut in half on the sides
• 2 cups grated Gruyere (about 170 g)
• 2 tbsp. l. grated parmesan
• Dijon mustard, lettuce leaves and French fries, for serving (optional)

Preparation:

1. Heat the olive oil in a large skillet over medium-high heat. Add the onion and cook, stirring, until it begins to darken, 3-4 minutes. Add the sugar and 1/2 teaspoon salt, reduce the heat to medium, and cook, stirring occasionally, until deep golden brown, another 15 minutes. Add the chicken broth and 1 teaspoon Worcestershire sauce and cook until the onion is softened and the liquid has almost completely evaporated, 8 minutes.
2. Preheat the oven to broil. In a large bowl, combine the ground beef, onion powder, and the remaining 2 tablespoons Worcestershire sauce. Form four 2-cm-thick patties and place them on a baking sheet. Use your thumb to make an indentation in the center of each patty; sprinkle with salt. Grill, turning once, for 5 minutes.
3. Place the buns cut-side up on a baking sheet. Sprinkle with both types of cheese and broil until the cheese is melted, about 1 minute. Spread mustard on the buns; sandwich the patty, lettuce, and caramelized onions between the bun halves. Serve with potato chips.