Caramelise the Onions: Melt the butter in a large frying pan over a low-medium heat. Add the sliced onions and a pinch of salt. Cook slowly, stirring occasionally, for 15-20 minutes until they are soft, golden, and sweet. Don't rush this part!

Finish the Onions: Once the onions are deeply golden, stir in the brown sugar and balsamic vinegar. Cook for another 2-3 minutes until the vinegar has reduced and the onions are sticky and jam-like. Scrape them out of the pan and set aside.

Prepare the Steak: Pat the steak dry with a paper towel – this is crucial for getting a good crust. Rub it all over with the olive oil and season very generously with sea salt and black pepper.

Cook the Steak: Place the same frying pan back on a high heat. When it's smoking hot, carefully lay the steak in the pan. Cook for 2-3 minutes per side for medium-rare, or longer depending on your preference and the thickness of the cut. For a deeper understanding of why a hot pan is so important, Serious Eats has a great guide on the Maillard reaction.

Rest the Steak: This is the most important step! Transfer the cooked steak to a cutting board and let it rest for at least 10 minutes. This allows the juices to redistribute throughout the meat, ensuring it's tender and juicy when you slice it.

Prepare the Bread: While the steak rests, slice your ciabatta rolls in half horizontally. I find that what works best for me is to toast them lightly under the grill or in the hot pan for a minute or two until golden. Once toasted, rub the cut side of each piece of bread with the raw garlic clove to impart a subtle flavour.

Slice the Steak: After resting, slice the steak thinly against the grain. You'll see the lines of the muscle fibres; make sure you cut across them, not parallel to them. This makes the meat much more tender to eat.

Assemble Your Sandwich: Mix the mayonnaise and mustard together. Spread this mixture over the bottom half of each ciabatta roll. Top with a generous layer of the caramelised onions, followed by the sliced steak. Pile the grated cheddar on top of the steak and place under a hot grill for 1-2 minutes, just until the cheese is melted and bubbling. Finish with a handful of fresh rocket and place the top of the roll on. Slice in half and serve immediately.