Mujadara (Lentils and Rice with Caramelized Onions)

Name: Mujadara (Lentils and Rice with Caramelized Onions)
Prep time: 10 min
Cook time: 50 min
Total time: 1 h
Cuisine: Middle Eastern
Ingredients: 5 Tbsp. extra-virgin olive oil, divided; 3 yellow onions; 1 and ½ tsp. ground cumin; 1 and ½ tsp. ground coriander; 1 tsp. cinnamon; 1 tsp. kosher salt; 1 cup brown or green lentils; 4 cups water or broth (use vegetable broth to keep the dish vegetarian); 1 cinnamon stick (optional); 1 and ¼ cups long-grain white rice, such as Basmati, rinsed in several changes of cold water; 2 Tbsp. butter; Juice of one lemon; Freshly ground black pepper, to taste