Prep the Meat: Season both sides of the steak with salt and pepper.
Sear the Steak: Heat a large skillet over medium-high heat, add oil, and sear the steak on both sides until browned (2-3 minutes per side). Remove and set aside.
Sauté the Vegetables: Lower the heat to medium, add sliced onions, carrots, and celery to the skillet, and sauté until softened (about 5 minutes).
Make the Roux: Sprinkle flour over the vegetables, stirring to combine. Cook for 2-3 minutes to create a roux.
Add Liquid: Gradually pour in beef broth while stirring, scraping up browned bits from the pan. Add Worcestershire sauce and garlic powder. Bring to a simmer and let thicken for 5-7 minutes.
Combine Steak and Gravy: Return the browned steak to the pan, nestling it into the gravy. Cover, reduce heat to low, and simmer for 45-60 minutes until fork-tender.
Slow Cooker Option: If using a slow cooker, transfer the seared steak and sautéed veggies into it. Add the broth mixture, cover, and cook on low for 6-8 hours or high for 3-4 hours.
Adjust Seasoning: Taste the gravy and adjust seasoning as needed.
Serve: Slice the steak against the grain and serve with mashed potatoes, egg noodles, or rice, topped with the rich brown gravy.