Season the beef shanks generously with salt, pepper, and all-purpose seasoning. Allow them to sit for about 20–30 minutes so the seasoning can penetrate the meat.

Heat oil in a large Dutch oven over medium-high heat. Place the beef shanks in the hot pan and sear each side until a deep brown crust forms. This step creates the flavor base for the sauce.

Remove the beef from the pot and set it aside. In the same pot, add the diced onion, celery, and carrots. Cook for several minutes until the vegetables begin to soften and lightly caramelize.

Add the minced garlic along with the rosemary and thyme. Stir continuously for about 30 seconds until fragrant.

Pour in the beef broth and bone broth while scraping up any browned bits stuck to the bottom of the pot. Those bits contain a lot of flavor and help build the sauce.

Return the beef shanks to the pot and bring the liquid to a gentle simmer. Cover and transfer the pot to a 325°F oven.

Allow the beef to braise for about 2½ to 3 hours, or until the meat is extremely tender and easily pulls away from the bone.

Once cooked, remove the beef from the pot and strain the braising liquid if desired. Bring the liquid to a simmer and stir in a cornstarch slurry to thicken the sauce slightly. Serve the beef over mashed potatoes or polenta and spoon the rich sauce over the top.