Heat olive oil in a Dutch oven over medium heat. Add diced onions and minced garlic, sautéing until softened and fragrant.
Add oxtail pieces to the pot, searing on all sides until browned.
Stir in chopped carrots and celery, cooking for an additional 2-3 minutes.
Pour in beef broth and red wine (if using), scraping any browned bits from the bottom of the pot.
Add bay leaves, salt, and pepper to taste. Bring the mixture to a simmer.
Reduce heat to low, cover, and let the stew simmer gently for 3-4 hours, or until the meat is tender and falling off the bone.
Once cooked, remove the bay leaves and discard.
Serve the oxtail stew hot, garnished with chopped fresh herbs for added flavor and freshness.