Pat the chuck roast dry with paper towels and season generously on all sides with salt and pepper. In a large skillet, heat 1 tablespoon olive oil over medium-high heat. Sear the beef until deeply browned on all sides, about 3-4 minutes per side. Transfer to a 6-quart slow cooker.

Reduce heat to medium. Add the remaining 1 tablespoon olive oil to the skillet. Add the sliced onion and cook, stirring often, until softened and starting to brown, about 5 minutes. Stir in the minced garlic and cook 1 minute more.

Pour the red wine into the skillet, scraping up any remaining browned bits from the bottom. Simmer until the wine is reduced by half, about 2 minutes. Pour the mixture over the beef in the slow cooker. Add the beef broth, Worcestershire sauce, rosemary, thyme, and bay leaves. The liquid should come about halfway up the sides of the roast; add a bit more broth if needed.

Cover and cook on LOW for 6-8 hours or on HIGH for 3-4 hours, until the beef is fall-apart tender, shreds easily with two forks, and has reached an internal temperature of at least 145°F (63°C) for food safety.

Transfer the cooked beef to a cutting board and shred with two forks, discarding any large pieces of fat. Strain the cooking liquid through a fine-mesh sieve into a fat separator or a bowl; discard solids. Let the liquid settle, then skim off the fat. Return shredded beef to the slow cooker, moisten with about 1/2 cup of the strained jus, and keep warm. Pour the remaining jus into a serving bowl or individual ramekins.

Preheat the broiler. Spread the cut sides of the rolls with butter and arrange on a baking sheet. Broil just until golden, about 1-2 minutes. Pile a generous amount of warm shredded beef onto the bottom half of each roll, drape with 2 slices of provolone, and return to the broiler for 30-60 seconds to melt the cheese. Close the sandwiches, sprinkle a pinch of flaky salt over the top, and serve immediately with hot au jus on the side.