Place each thin beef slice between two sheets of baking paper or cling film. Gently flatten the meat with a meat mallet or rolling pin until it is an even thickness, taking care not to tear it. Season both sides with salt and black pepper. If the beef slices are already thin and tender, you may only need to flatten the thicker areas slightly.

In a mixing bowl, combine the sausage meat, fresh breadcrumbs, finely chopped onion, parsley, thyme, and English mustard. Season lightly with salt and black pepper, then mix until the ingredients are evenly distributed. The stuffing should hold together when pressed but remain soft. Divide it into four equal portions so each beef olive has a similar amount of filling.

Place one portion of stuffing along the centre of each beef slice. Fold in the sides slightly, then roll the beef firmly around the filling to create a neat parcel. If using bacon, wrap a slice around each roll before securing it. Tie each beef olive with kitchen string or use toothpicks to hold it closed. Make sure the stuffing is enclosed as much as possible.

Heat the vegetable oil in a large frying pan or casserole pot over medium-high heat. Add the beef olives and brown them on all sides, turning carefully with tongs. This should take around 6–8 minutes in total. The beef does not need to be cooked through at this stage; browning simply develops a rich colour and adds flavour to the gravy. Transfer the rolls to a plate.

Add the sliced onion and diced carrot to the same pan, cooking for 4–5 minutes until softened. Stir in the tomato purée and plain flour, then gradually add the beef stock while stirring to prevent lumps. Add the Worcestershire sauce and bay leaf. Return the beef olives to the pan, cover, and simmer gently for 75–90 minutes, or until the beef is tender. Alternatively, braise in a covered oven-safe dish at 160°C (320°F).

Check that the beef is tender and the stuffing is fully cooked. Carefully remove the beef olives from the gravy and take out the kitchen string or toothpicks before serving. If the gravy is too thin, simmer it uncovered for a few minutes until it reaches your preferred consistency. Stir in a little butter for extra richness if desired, then spoon the gravy over the beef olives and serve hot.