Season the chuck roast generously with salt and pepper. Heat the beef tallow in a large Dutch oven over medium-high heat. Add the roast and sear until deeply browned on all sides, 3 to 4 minutes per side. Transfer to a plate.

Add the onions to the pot and cook, stirring occasionally, until softened and lightly browned, about 8 minutes. Return the roast to the pot and add the garlic, rosemary and thyme.

Pour in the chicken broth and Worcestershire sauce and bring to a simmer. Place a piece of parchment paper directly over the surface of the liquid. Cover the pot and transfer to the oven. Braise until the beef is very tender and pulls apart easily with a fork, about 3 hours.

Meanwhile, make the caramelized onions. Melt the butter with the olive oil in a large skillet over medium-low heat. Add the onions and salt and cook, stirring occasionally, until deeply golden and soft, 40 to 50 minutes. Add a splash of water if the onions begin to stick. Stir in the sugar, if using, during the final few minutes.

Transfer the beef to a cutting board and let cool slightly. Strain the braising liquid through a fine-mesh strainer into a saucepan. Skim the fat from the surface and keep the au jus warm.

Shred the beef into large pieces, discarding any excess fat and connective tissue.

Heat the broiler. Lightly butter the cut sides of the rolls and place them cut-side up on a baking sheet. Broil until lightly toasted, 1 to 2 minutes.

Divide the beef among the rolls and top with the provolone. Broil until the cheese is melted and bubbling, 1 to 2 minutes.

Top with the caramelized onions and serve with the warm au jus for dipping.