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