Lentil Soup with Beef

2 tablespoons olive oil
1 1/2 pounds boneless beef chuck, cut into 1-inch cubes
Salt and freshly ground black pepper
3 large celery stalks, chopped
2 large carrots, peeled and chopped
1 large onion, chopped
6 garlic cloves, chopped
1 1/2 teaspoons chopped fresh rosemary leaves
1 1/2 teaspoons dried oregano
6 (14-ounce) cans beef broth
1 (28-ounce) can diced tomatoes in juice
2 cups (about 11 ounces) lentils, rinsed
1/3 cup chopped fresh Italian parsley leaves

Heat the oil in heavy large pot over medium-high heat. Sprinkle the beef with salt and pepper. Add half of the beef and cook until brown, about 8 minutes. Using a slotted spoon, transfer the beef to a bowl. Repeat with the remaining beef. Add the celery, carrots, onion, garlic, rosemary, and oregano to the pot. Saute until the onions are translucent, about 8 minutes.

Return the beef and any accumulated juices from the bowl to the pot. Add the broth and tomatoes with their juice. Bring the soup to a boil. Reduce the heat to medium-low. Cover and simmer until the meat is just tender, stirring occasionally, about 1 hour.

Add the lentils. Cover and continue simmering until the lentils are tender, about 40 minutes. Stir in the parsley. Season the soup, to taste, with salt and pepper. Ladle the soup into bowls and serve.