Cook the Pasta: Bring a large pot of salted water to a rolling boil. Add the pasta and cook according to package directions until al dente. Just before draining, reserve about 250ml (a cupful) of the starchy pasta water. Drain the pasta and set aside.

Sear the Beef: While the pasta is cooking, pat the thinly sliced steak dry with paper towels and season generously with salt and pepper. Heat the olive oil in a large, heavy-based frying pan or skillet over a high heat. Once shimmering, add the steak in a single layer (work in batches if necessary to avoid overcrowding) and sear for 1-2 minutes per side until nicely browned. Remove the beef from the pan and set it aside on a plate.

Sauté the Vegetables: Reduce the heat to medium and add the sliced onion to the same pan. Cook for 5-7 minutes, stirring occasionally, until softened and starting to caramelise. Add the sliced mushrooms and cook for another 5 minutes until they've released their liquid and are turning golden brown.

Build the Flavour Base: Add the minced garlic to the pan and cook for 1 minute until fragrant. Sprinkle the plain flour over the vegetables and stir continuously for 1 minute to cook out the raw taste.

Create the Sauce: Slowly pour in the beef stock, stirring constantly to scrape up any browned bits from the bottom of the pan. Let it bubble for a minute to thicken slightly. Stir in the double cream and Worcestershire sauce, then bring to a gentle simmer.

Melt the Cheese: Reduce the heat to low. Add the grated Cheddar and Provolone cheeses to the pan. I find that stirring gently and consistently until the cheese is fully melted and the sauce is smooth works best here. Avoid letting the sauce boil, as this can cause it to split. Season with salt and pepper to your taste.

Combine Everything: Return the seared beef (and any juices from the plate) to the sauce. Add the drained pasta to the pan.

Finish and Serve: Toss everything together until the pasta and beef are completely coated in the creamy sauce. If the sauce seems too thick, add a splash of the reserved pasta water to loosen it to your desired consistency. Serve immediately, garnished with fresh parsley if you like.