Preheat and Sear the Mock Tenderloin: Preheat the oven to 300°F (150°C). Heat your Dutch oven over medium-high heat and add the olive oil. While the oil heats up, season the mock tenderloin generously with salt and pepper. Once the oil is shimmering, place the meat in the Dutch oven and sear it for about 3-4 minutes on each side until it forms a rich, golden-brown crust. Remove the tenderloin from the pot and set it aside.
Sauté Aromatics: In the same Dutch oven, add the sliced onions, minced garlic, carrots, and celery. Sauté the vegetables for 5-7 minutes until they begin to soften and release their aroma. Stir in the tomato paste and cook for an additional 2 minutes to deepen its flavor.
Deglaze and Add Braising Liquid: Once the vegetables are softened, pour in the beef broth and red wine (if using). Scrape the bottom of the pot with a wooden spoon to lift up any flavorful browned bits from the meat. Add the thyme, rosemary, and bay leaves. Stir well to combine.
Braise the Meat: Return the seared mock tenderloin to the pot, ensuring it is mostly submerged in the liquid. Add water as needed to cover the meat. Bring the mixture to a simmer over medium heat, then cover the Dutch oven with its lid and transfer it to the preheated oven. Braise the meat for 2 to 2.5 hours, or until the mock tenderloin is fork-tender and easily pulls apart.
Final Touches and Serve: Once the mock tenderloin is done braising, remove it from the oven and let it rest for 5 minutes. If you prefer a thicker sauce, place the braising liquid over medium heat on the stovetop and simmer until it reduces to your desired consistency. Slice the tenderloin and serve it with the braising sauce. Pair with mashed potatoes, roasted vegetables, or your preferred side.
