Slow-Cook the Beef
Pat dry and rub with olive oil, smoked paprika, garlic powder, onion powder, salt and pepper.
Place into a slow cooker, dd the beef stock, Worcestershire sauce and tomato purée and cook on LOW for 7–8 hours or HIGH for 4–5 hours until the beef is tender and pulls apart easily.
Remove the beef from the cooker and shred with two forks. Mix with a few spoonfuls of the cooking juices. Set aside.
Make the Toasties
Lightly butter one side of each slice of bread.
Place the bread butter-side down.
Spread a thin layer of mustard on half the slices.
Top with a spoonful of pulled beef, season lightly, and sprinkle with grated cheese.
Add the top slices of bread (butter-side facing out).
Toast in a sandwich press or frying pan for 2–3 minutes per side until golden and the cheese is melted.
Cut into halves or quarters and serve warm with pickles and gravy for dipping.