Caramelise the Onions: Heat the olive oil in a large, heavy-bottomed frying pan over medium-low heat. Add the sliced onions and half the salt. Cook slowly, stirring occasionally, for 15-20 minutes, until they are soft, deeply golden, and sweet. Remove from the pan and set aside.

Sear the Steak: Increase the heat to high. Add the thinly sliced steak to the hot pan in a single layer (you may need to do this in two batches). Season with the remaining salt and pepper. Cook for just 1-2 minutes per side until just browned. It will cook further inside the egg roll, so don't overdo it.

Combine the Filling: Remove the steak from the pan and place it on a chopping board. Roughly chop it into small, bite-sized pieces. In a large bowl, combine the chopped steak, caramelised onions, Worcestershire sauce, and the grated provolone cheese. Mix everything together until well combined.

Cool the Filling: Spread the filling out on a plate or baking tray and let it cool for at least 10 minutes. A warm filling can make the wrappers soggy and cause them to tear. I find that popping it in the fridge during this time works wonders.

Assemble the Egg Rolls: Place an egg roll wrapper on a clean surface in a diamond shape (with one corner pointing towards you). Spoon about 2-3 tablespoons of the cooled filling in a line across the centre. Fold the bottom corner up and over the filling, tucking it in tightly. Fold in the left and right corners towards the centre, like an envelope. Dab a little water on the top corner and roll it up tightly to seal. Repeat with the remaining wrappers and filling.

Heat the Oil: Pour the rapeseed oil into a deep, heavy-bottomed pot or Dutch oven until it's about 5cm deep. Heat over medium-high heat until it reaches 180°C (350°F). Use a kitchen thermometer for accuracy.

Fry the Egg Rolls: Carefully place 3-4 egg rolls into the hot oil, making sure not to overcrowd the pot. Fry for 3-5 minutes, turning occasionally, until they are a deep golden brown and crisp all over.

Drain and Serve: Use tongs to remove the cooked egg rolls from the oil, allowing any excess to drip off. Place them on a wire rack to drain (this keeps them crispier than using paper towels). Serve them hot with your favourite dipping sauce.