INGREDIENTS 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 In a large skillet over […]
