Party sized French Dip sliders so good, no one will be able to resist them.
Add the oil in your slow cooker's insert if it is stove top safe, if it is not stove top safe, then heat the oil in a cast iron pan or dutch oven. Heat the oil over medium-high heat. Season the beef chuck roast on all sides with salt and pepper. Sear all sides of the meat in the oil over medium-high heat until each side has a nice brown crust. Remove and set aside on a plate. In the same pan, saute the onion for 3 - 5 minutes, until golden, adding more oil if necessary. Then add the garlic and saute for 1 minute. Add the meat and any juices that have collected on the plate along with the onion and garlic to the slow cooker. Add the bay leaves, Worcestershire, red wine, tomato paste, beef broth to the pan (or slow cooker insert if using). If you're using fresh thyme, add the sprigs during the last 30 - 60 minutes of cooking. If you're using dried thyme, add it at the same time as the beef broth. Cover with a lid and cook on low for 6-8 hours, or until the meat easily shreds using a fork. Remove the meat and shred it or cut in into thin slices, however you prefer. Set aside in a bowl. Ladle off excess fat from the top of the au jus and discard the fat. To make this easier, you can chill the liquid until the fat solidifies. Discard the bay leaves and thyme sprigs. Keep the remaining au jus in the slow cooker to keep warm while you prepare the sandwiches. If desired, you can thicken the jus with flour or cornstarch. After adding flour or cornstarch and whisking to combine, bring the mixture to a rolling boil. Then lower heat to keep warm.