01 - Scatter the thinly sliced onion and minced garlic across the bottom of the slow cooker, creating an even aromatic bed for the roast.
02 - Combine the kosher salt, black pepper, dried Italian seasoning, basil, and oregano. Rub the seasoning mixture evenly over all sides of the chuck roast, pressing gently to adhere.
03 - Place the seasoned chuck roast on top of the onion and garlic layer in the slow cooker.
04 - Pour the beef broth and pepperoncini juice over the roast. Sprinkle in the crushed red pepper flakes if using. The liquid should surround but not fully submerge the meat.
05 - Cover the slow cooker and cook on LOW for 8 hours or on HIGH for 5 to 6 hours, until the beef is fork-tender and shreds apart with minimal effort.
06 - Carefully remove the roast from the slow cooker and transfer to a large cutting board. Using two forks, shred the beef, discarding any large pieces of excess fat. Return the shredded meat to the slow cooker and toss thoroughly in the accumulated juices.
07 - If desired, spread softened butter on the cut sides of each sandwich roll. Place under the broiler cut-side up until golden and lightly crisped, about 1 to 2 minutes.
08 - Pile the shredded beef generously onto each toasted roll. Layer 2 slices of provolone cheese and a handful of sliced pepperoncini on top of each sandwich.
09 - For a finishing touch, place the assembled open-face sandwiches under the broiler for 1 to 2 minutes until the provolone is melted and bubbly. Serve immediately while warm.