Probably not the healthiest, but definitely amongst the tastiest

1. Get the pan hot, hot enough that when you add drop of water, it should dance. Try and use a non coated pot like a stainless steel.
2. Dice the onions and mushrooms. Mince 1 clove of garlic, keep the other as as whole.
3. Season the steak generously with salt and pepper and some oil. Add to the pan and don’t move it.
4. Let it sizzle for 1 minute, then flip the steak. It should have formed a brown crust. Add butter and whole garlic to the pan.
5. Baste the steak with the butter for about 1-2 minutes. Keep flipping the steak, this way it will cook evenly and not be grey in some spots and pink in the other.
6. Test for doneness (to however you like it, preferable medium-rare/medium) with a meat thermometer or by poking. Put the steak in a plate, cover with foil and let it rest.
7. Add some more butter to the same pan along with the onions and mushrooms. Add some salt and let them cook for about 5 mins.
8. In the meantime, prepare the pasta water for boiling. Remember to salt the water!
9. Once the onions and mushrooms are soft, add some stock and be sure to scrape any of the flavour stuck to the pan from that steak. Let it cook for a minute.
10. Add the cream, and black pepper to your liking. Let it cook for 10 minutes until the sauce thickens.
11. Boil the pasta according to the instructions on the packet and time it so its ready to add to sauce once done.
12. Add the mustard and the Worcestershire sauce, along with any of the steak resting juices in the bowl. Cook for 5 mins
13. Add the sour cream and mix, you should have a thick-ish consistency now in the sauce.
14. Add the pasta to the sauce, add pasta water if the sauce is too thick.
15. Slice the steak into thin strips, try and keep them as thin as possible. Add to the top of the pasta.
16. Garnish with coriander or parsley and serve.