Heat the olive oil in a large pot over medium heat. Add the beef and cook until browned on all sides, about 6 to 8 minutes.
Add the onion, carrots, and celery to the pot. Cook for 5 minutes, stirring occasionally, until the vegetables begin to soften.
Stir in the garlic and cook for 1 minute until fragrant.
Pour in the crushed tomatoes and beef broth. Add the lentils and rosemary sprigs. Bring the mixture to a boil.
Reduce the heat to low, cover the pot, and simmer for 45 to 50 minutes until the beef is tender and the lentils are cooked through.
Remove the rosemary sprigs. Taste and season with salt and black pepper as needed before serving.