Take the beef joint out of the fridge and leave it to come up to temperature.
Heat oven to 100 C / 80 C fan. Place the garlic and herbs in a roasting dish.
Place half of the beef dripping into a large frying pan and place over a medium-high heat. Add the sliced onions and fry until slightly golden then remove from the pan into the roasting dish. Return the pan to the heat and add the remaining half of the beef dripping.
Rub a tablespoon of salt over the meat, then add the beef joint to the pan, searing on each side until golden and caramelised, paying particular attention to the fat. Place the beef into the roasting dish, nestling on top of the onions, garlic and herbs and then place everything into the oven to roast for about 45 minutes - 1 hour, or until a digital read thermometer inserted into the thickest point of the joint reads about 56 - 58 C for medium rare.
Lift the beef onto a chopping board, reserving everything in the roasting tin and leave to rest for 20 mins. After 20 minutes remove the bone from the beef joint and cover the meat in tin foil to rest again.
To make the gravy, remove the herbs and garlic from the roasting then place the onions, and any juices into a large saucepan and stir in the flour. Add in anything that has collected on the resting chopping board, then slowly pour in the wine, scraping everything up from the bottom of the pan, add the beef stock cube, water, dijon and the Worcestershire sauce and stir. Add the bone you removed from the beef and leave to simmer for 20 minutes, then strain into a small pan and keep warm, reserving the onions. Place the onions into a small bowl.
To assemble your sandwiches, slice the rolls in half lengthways and toast in a pan on the cut side. Slice your meat very thinly across the grain and then pile on to the roll. Divide the onions between the rolls and lay a few slices of swiss cheese on top of the onions and place the lid of the roll on top of the cheese. Place the sandwiches into the oven for 3 - 5 minutes to slightly melt the cheese then serve hot with the gravy on the side for dipping.