Season lamb shanks with salt and pepper, then sear in olive oil over medium-high heat until browned on all sides.
Remove lamb, then sauté onion, carrots, celery, and garlic until softened.
Stir in tomato paste and cook for 2 minutes, then deglaze with red wine.
Add beef stock, rosemary, thyme, and bay leaves. Bring to a simmer.
Return lamb to the pot, cover, and transfer to a 325°F oven for 2.5 to 3 hours.
Remove lamb and strain the sauce. Simmer to reduce or thicken with a cornstarch slurry.
Serve shanks with the herb-infused gravy over mashed potatoes or polenta.
