First your meat must be room temperature.
Filet must be cut into at least 2,5 cm steaks across the grain after all sinew and membranes removed with a sharp knife.

Heat a heavy based frying pan.
Add enough oil to cover the bottom completely.
Put a large knob of butter into the oil.
Season the filet steaks lightly on both sides and put into the bubbling oil and butter.
Fry for about 3 mins over high heat, turn over and fry the other side for another 2-3 minutes.
This will give you a medium rare steak.
Remove from the pan and put in warm plate to rest for a few minutes.

Serve with sauce of your choice, chips, salad or vegetables.