1. Take the steaks out of the fridge ahead of time to let them reach room temperature before cooking.
2. Heat the oil in a frying pan, then fry 2-5 minutes each side depending on the thickness of your steak and whether you prefer your steak rare, medium or well done.
3. Check the steak is cooked to your preference by touch – rare: soft, medium: bouncy, well done: firm.
3. Season the steak, turn off the heat, and put on one side to rest for a maximum of 5 minutes to allow the juices to be reabsorbed into the meat fibres and tenderise the beef.
3. Meanwhile, pour the crème fraiche into a saucepan and heat through.
4. Take off the heat and add the mustard. Mix well and return to the heat.
5. Heat through until bubbling. Turn heat to very low until the steaks have rested.
6. Serve.
Slice steak thinly, mix with the sauce and serve with lettuce in wraps.