01 -
Peel and thinly slice the yellow and sweet onions into rings. Mince the garlic cloves.
02 -
Set the slow cooker to high heat. Add butter, onions, garlic, brown sugar, and balsamic vinegar. Stir to combine, cover, and cook for 20 to 30 minutes until onions soften and begin to caramelize. Alternatively, sauté onions in a skillet for 10 minutes and transfer them to the cooker.
03 -
Pat the chuck roast dry and season evenly with kosher salt and black pepper. Heat olive oil in a skillet over medium-high heat and sear the roast for 2 to 3 minutes on each side until well browned. This step is optional but enhances flavor.
04 -
Nestle the seared roast on top of the caramelized onions in the slow cooker. Sprinkle dried or fresh thyme and bay leaves evenly over the roast and onions.
05 -
Pour beef broth, white wine (or additional broth), and Worcestershire sauce into the slow cooker. Ensure the roast is partially submerged by adding more broth if necessary.
06 -
Cover and cook on low for 8 to 9 hours or on high for 5 to 6 hours until the meat is fork-tender and shreds effortlessly. Begin checking for doneness after 7 hours.
07 -
Remove the roast from the slow cooker and tent with aluminum foil to rest. Skim excess fat from the cooking liquid. Combine cornstarch with cold water to create a slurry, then stir it into the liquid. Cook uncovered on high for 10 to 15 minutes until the gravy thickens.
08 -
Slice or shred the rested meat and return it to the slow cooker, spooning the onion gravy over the top. Optionally, sprinkle with shredded Gruyère or Swiss cheese and garnish with chopped parsley. Serve hot directly from the cooker or plated.