Directions

1. Preheat an oven to 325 degrees F (165 degrees C).
2. Melt the butter in a large skillet over medium heat. Cook and stir the onion in the melted butter until softened, about 5 minutes. Stir the ketchup, lemon juice, Worcestershire sauce, brown sugar, and yellow mustard into the onion and butter; allow mixture to warm completely.
3. Heat a separate skillet over medium-high heat. Season the steaks with salt and black pepper; cook in the skillet until browned on each side, 3 to 4 minutes per side. Transfer the steaks to a 9x13-inch baking dish. Pour the sauce from the skillet over the steaks.
4. Bake in the preheated oven until meat is cooked through and no longer pink in the middle, about 1 hour.
5. Transfer the steaks from the baking dish to a platter, shaking any excess sauce from the meat. Stir the cornstarch and water together until smooth in a small bowl, then mix into the hot sauce remaining in the baking dish until the mixture begins to thicken; pour over the steaks to serve.