Pat beef dry and season with salt and pepper.
- Heat olive oil in a large skillet or Dutch oven over medium-high heat. Sear beef in batches until browned on all sides; remove and set aside.
- Add onion, carrots, and celery to the pot; sauté until softened. Stir in garlic and cook for 1 minute.
- Sprinkle flour over vegetables; cook 1–2 minutes, stirring to coat.
- Slowly pour in Merlot, scraping up browned bits. Simmer 2–3 minutes to cook off alcohol.
- Stir in beef broth, tomato paste, Worcestershire sauce, thyme, and bay leaf.
- Return beef to the pot. Reduce heat to low, cover, and simmer 1½–2 hours, until beef is fork-tender.
- Remove bay leaf, adjust seasoning, and serve hot over mashed potatoes, noodles, or rice.