Preheat oven to 325°F (165°C).
Coat steaks in flour, salt, pepper, and garlic powder. Brown in oil in a large oven-safe pot. Remove and set aside.
Sauté onion, celery, pepper, and mushrooms in the same pot. Add garlic and tomato paste; cook 1–2 minutes.
Add tomatoes, broth, Worcestershire, thyme, sugar, and celery seed. Stir and return steak to pot.
Cover and bake for 1½ to 2 hours, until steak is fork-tender.
Optional: Thicken gravy by mixing cornstarch with water, stirring it into the pot, and simmering until thickened.
Serve hot over mashed potatoes, egg noodles, or rice.