Prepare the Beef: Pat the beef steak dry with paper towels and season generously with salt and pepper on both sides.

Sear the Steak: In a large, heavy-bottomed pot or Dutch oven, heat the olive oil over medium-high heat. Add the beef steak to the pot and sear for about 4-5 minutes on each side, or until browned. Remove the steak from the pot and set aside.

Caramelize the Onions: In the same pot, add the sliced onions. Lower the heat to medium and cook the onions, stirring often, until they are soft and caramelized, about 15-20 minutes. Add the minced garlic and cook for an additional 1-2 minutes until fragrant.

Deglaze the Pot: Pour in the red wine (or additional beef broth) to deglaze the pot, scraping up any browned bits from the bottom. Let it simmer for about 3-4 minutes.

Add Remaining Ingredients: Stir in the beef broth, Worcestershire sauce, Dijon mustard, brown sugar, dried thyme, bay leaf, and return the seared beef steak to the pot.

Braise the Beef: Bring the mixture to a simmer, then cover the pot with a lid and reduce the heat to low. Allow the beef to braise for 2 to 3 hours, or until it is tender and easily shreds with a fork.

Finish the Gravy: Once the beef is done, remove it from the pot and let it rest for a few minutes. Meanwhile, increase the heat to medium-high and let the gravy reduce slightly to thicken, if desired. Adjust seasoning with salt and pepper to taste.

Serve: Slice the beef steak against the grain and serve it topped with the caramelized onion gravy. Garnish with chopped fresh parsley.