01 - Preheat the oven to 400°F (200°C) and line a baking tray with parchment paper.
02 - Heat sunflower oil in a skillet over medium-high heat. Add the diced steak and sear for 2 to 3 minutes until evenly 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 Worcestershire sauce, English mustard if using, sea salt, and black pepper. Remove from heat and let the mixture cool slightly.
05 - Unroll the puff pastry sheet onto a lightly floured surface and cut into four equal rectangles.
06 - Spoon the steak mixture evenly along one long side of each pastry rectangle. Top each portion with grated cheddar cheese.
07 - Fold the pastry over the filling, pinch the edges firmly to seal, and place each roll seam-side down on the prepared baking tray.
08 - Brush each roll with beaten egg to ensure a rich golden finish during baking.
09 - Bake for 20 to 25 minutes until the pastry is puffed and deep golden brown. Allow to cool slightly before serving.