Brown the beef in batches. Heat 1 tablespoon of oil in your large pot over a high heat. Add half the beef strips in a single layer—don't overcrowd the pot. Let them sizzle undisturbed for 2 minutes until the underside is a deep, rich brown colour and you can smell that wonderful caramelisation. Use tongs to flip the strips and cook for another minute. The beef should be browned on the outside but still pink within. Transfer to a plate and repeat with the remaining oil and beef. Set the beef aside.

Softe the vegetables. Reduce the heat to medium. Add the sliced onion to the pot and cook for 4-5 minutes, stirring occasionally. The onion will soften and turn translucent, and you'll hear a gentle hiss as it releases its moisture. Add the minced garlic and cook for 30 seconds until it smells fragrant and aromatic.

Cook the mushrooms. Tip in the sliced mushrooms and stir well. Cook for 5-6 minutes, stirring every now and then. The mushrooms will first release their liquid—you'll see it pooling at the bottom of the pot—and then that liquid will evaporate, leaving the mushrooms golden and slightly shrunken. You should hear a gentle sizzle as the moisture disappears.

Build the base of the sauce. Sprinkle the plain flour over the vegetables and stir constantly for 1 minute. This will cook out the raw flour taste and help thicken the sauce later. Add the tomato purée and smoked paprika, stirring for another 30 seconds until everything is well combined and smells earthy and rich.

Add the liquid and pasta. Pour in the beef stock, scraping the bottom of the pot with a wooden spoon to lift any browned bits (that's where the flavour lives). Add the Dijon mustard and a good pinch of salt and pepper. Bring the liquid to a gentle boil—you'll see small bubbles breaking the surface. Break the tagliatelle in half and add it to the pot, pressing it down so it's submerged in the liquid.

Simmer the pasta. Reduce the heat to a low simmer. Cook for 10-12 minutes, stirring occasionally to prevent the pasta from sticking. The liquid will gradually be absorbed, and the pasta will swell and become tender. You'll notice the sauce thickening and becoming glossy. When you taste a piece of pasta, it should be al dente—firm to the bite but not hard in the centre.

Finish the dish. Return the browned beef and any juices from the plate to the pot. Stir gently and cook for 2 minutes until the beef is heated through. Remove the pot from the heat. Pour in the double cream and add the crème fraîche, stirring until the sauce is smooth and velvety. Taste and adjust the seasoning with more salt and pepper if needed. The sauce should coat the back of a spoon.

Serve immediately. Divide the stroganoff among warm bowls. Garnish with a generous sprinkle of fresh parsley. The pasta will be tender, the beef juicy, and the sauce luxuriously creamy.