Generously season the beef roast with salt and pepper then add the butter and olive oil to a large skillet and sear well on both sides then place in the slow cooker.
In the same skillet add the onions, lightly season with salt and pepper and cook 3-4 minutes or until the onions have softened.
Pour in the Worcestershire sauce, soy sauce, beef stock and package of au jus to the skillet whisking until it’s completely blended then pour over the roast. Top with the rosemary sprig and cook 3-4 hours on HIGH 5-6 hours on LOW. The beef is done when it’s very tender and able to easily slice. Continue cooking if you prefer it shredded.
Remove from the slow cooker and slice the beef as thinly as possible.
Cut the rolls in half, butter the inside of each, place on a baking sheet and bake 5 minutes at 400°. Remove from the oven then layer the sliced beef onto the bottom half of each roll, divide the onions between them and top with provolone cheese. Broil 1-2 minutes or until the cheese is melted.Serve with individual small bowls of au jus for dipping.