Heat olive oil in a large, heavy-bottomed pot over medium-high heat. Add ground lamb and cook until browned and crisp bits form, breaking it into pieces.

Add onion, celery, and carrot; sauté about 5 minutes until soft.

Mix in tomato paste, bay leaves, rosemary, thyme, salt, and pepper; cook 5 minutes to deepen flavor.

Stir in chicken stock and diced tomatoes; bring to a boil, then reduce heat to low. Cover partially and simmer 2–2½ hours, stirring occasionally, until thickened and rich.

Near the end, cook pappardelle in salted boiling water until al dente; drain.

Toss pasta with a few ladles of ragu, serve topped with additional sauce and Parmesan.