Step 1: Pat the beef chuck roast completely dry with paper towels. Season generously all over with 2 tsp salt and 1 tsp black pepper.
Step 2: Heat 1 tablespoon of olive oil in a large, heavy-bottomed skillet or Dutch oven over medium-high heat. Carefully add the beef and sear for 3-5 minutes per side until deeply golden brown. Remove the seared beef and set aside.
Step 3: Add the remaining tablespoon of olive oil to the same skillet. Add the chopped onion and cook until softened, about 5-7 minutes. Stir in the minced garlic and cook for another minute until fragrant.
Step 4: Pour in the red wine (if using) or 1/4 cup of beef broth to deglaze the pan, scraping up any browned bits from the bottom with a wooden spoon. Cook for 2-3 minutes until the liquid reduces slightly.
Step 5: Transfer the seared beef to your slow cooker. Add the sautéed onions and garlic mixture from the skillet. Stir in the tomato paste, Worcestershire sauce, dried thyme, dried rosemary, and bay leaves.
Step 6: Pour in the 3 cups of beef broth. Ensure the liquid comes about halfway up the sides of the beef. If desired, you can add chopped carrots or potatoes around the beef at this stage.
Step 7: Cover the slow cooker and cook on low for 6-8 hours or on high for 3-4 hours, until the beef is incredibly tender and easily shredded with a fork.
Step 8: Once cooked, carefully remove the beef from the slow cooker and transfer it to a cutting board. Tent loosely with foil and let it rest for 10-15 minutes. Discard the bay leaves from the cooking liquid.
Step 9: (Optional, for thicker gravy) Skim any excess fat from the surface of the cooking liquid. In a small bowl, whisk together 2 tablespoons of cornstarch with 2 tablespoons of cold water to create a slurry. Stir the slurry into the hot cooking liquid in the slow cooker. Cook on high for another 15-20 minutes, stirring occasionally, until the gravy has thickened to your desired consistency.
Step 10: Shred the tender beef using two forks. Return the shredded beef to the thickened gravy in the slow cooker, stirring to coat. Let it sit for a few minutes to absorb the flavors before serving. Enjoy your delicious slow cooker beef recipe!