Preheat oven to 300°F. Pat the chuck roast completely dry with paper towels, then season generously on all sides with salt and pepper.
Sear the meat by heating 1 tablespoon olive oil in a large Dutch oven over medium-high heat. Add the roast and sear for 5 minutes per side until deep golden brown on all sides. Remove and set aside.
Caramelize onions by adding 2 tablespoons olive oil to the same pot. Add sliced onions with a pinch of salt and cook over medium heat for 5 minutes, then reduce to medium-low and cook 20-25 minutes, stirring occasionally, until deep golden brown.
Add aromatics by stirring in minced garlic and maple syrup. Cook 7-8 minutes until fragrant and caramelized, then sprinkle flour over onions and stir for 1 minute.
Deglaze by pouring in red wine and scraping the bottom of the pot with a wooden spoon to release all browned bits. Let bubble for 1 minute.
Add liquid by stirring in beef broth, thyme sprigs, and bay leaf. Bring to a simmer, then nestle the seared roast into the onion mixture. Liquid should come about two-thirds up the meat.
Braise by covering the pot tightly with a lid and transferring to the oven. Cook for 3 hours, then check for tenderness. Flip the roast and gently pull it apart slightly with two forks. Re-cover and cook another 30 minutes until fork-tender.
Rest and serve by removing pot from oven and letting sit 10-15 minutes. Discard thyme sprigs and bay leaf. Shred meat and serve with plenty of the onion sauce.
