Blue Cheese Burgers with Caramelized Onions and Crispy Rosemary

• 3 tbsp. extra-virgin olive oil
• 4 Fresh rosemary sprigs
• 2 medium red onions, thinly sliced into half-moons
• 1 tsp. kosher salt, divided
• 1 1/2 lb. ground chuck
• 1/2 tsp. Freshly ground black pepper
• 4 oz. blue cheese (about 1 cup, crumbled)
• 4 Hamburger buns
• 8 butter lettuce leaves

DIRECTIONS

1. In a large skillet over medium heat, heat oil. Add rosemary and fry for about 1 minute, or until the leaves are crispy. Use tongs to pluck the sprigs out of the oil and place on a paper towel. When cool enough to handle, pull the leaves from the sprigs.
2. Add the onions and 1/4 teaspoon of the salt to the skillet and stir to coat. Cover and let cook, undisturbed, for 7 to 8 minutes, until they start to soften. Remove the lid and continue to cook until softened and caramelized, stirring occasionally, 7 to 8 minutes more. Remove from the heat and stir in the rosemary leaves.
3. Preheat the oven (with the oven rack in the middle) to 400°. Shape the beef into 4 patties about 3/4″ thick. Sprinkle both sides with pepper and the remaining 3/4 tea­spoon salt.
4. Heat a large skillet, preferably cast-iron, over medium heat. Add the patties and cook for 5 to 6 minutes, until the undersides have a nice dark brown crust. Flip the patties and cook for 5 to 6 minutes more for medium doneness. (Sorry about the splatters!!)
5. Transfer the burgers to a rimmed sheet pan. Dividing evenly, crumble the blue cheese over each burger. Bake until the cheese melts, 2 to 3 minutes. Warm your buns at the same time.
6. Build your burgers with the buns, patties, lettuce, caramelized onions and rosemary.