01 - Preheat the oven to 400°F (200°C) and line a baking tray with parchment paper.
02 - Heat the sunflower oil in a skillet over medium-high heat. Add the diced steak and sear for 2–3 minutes until well browned on all sides.
03 - Add the chopped onion to the skillet and cook for 2 minutes until softened. Stir in the minced garlic and cook for an additional 1 minute until fragrant.
04 - Stir in the Worcestershire sauce, English mustard (if using), sea salt, and black pepper. Remove from heat and allow the mixture to cool slightly.
05 - Unroll the puff pastry sheet onto a lightly floured surface. Cut into four equal rectangles.
06 - Spoon the steak mixture evenly along one long side of each pastry rectangle. Top each portion generously with grated cheddar cheese.
07 - Fold the pastry over the filling, pressing and pinching the edges firmly to seal. Place each roll seam-side down on the prepared baking tray.
08 - Brush the top of each roll with beaten egg to ensure a rich golden finish during baking.
09 - Bake for 20–25 minutes until the pastry is puffed and deep golden brown. Allow to cool for a few minutes before serving.