Fillet differs from other steak cuts in that it is incredibly lean and also cut to almost twice the thickness. Fillet cooked to well done is exceptionally dry; for that reason it is best served rare to medium. The best way to cook steak is by direct heat; either pan-fry or grill-pan. Non-stick is the enemy of meat; cast iron its friend.

Always bring steak to room temperature before cooking. Oil the meat and not the pan; just rub a little oil over the surface and season with freshly ground black pepper. Salt the pan and not the meat; throw a pinch of flaked sea salt into the pan before the meat. Make sure the pan is searingly hot; holding a hand flat above the surface is the best gauge.

Although times can vary according to thickness the following is a fairly accurate gauge for an average 1.75 inch thick steak;
Blue steak – 1.5 minutes on each side
Rare steak – 2.5 minutes on each side
Medium rare steak – 3.5 minutes on each side
Well done steak – 4.5 minutes each side

Due to its thickness you may find fillet is easier to finish off in a hot oven. A cast-iron pan will go from hob to grill effortlessly. After cooking a steak needs its rest; let it sit for at least five minutes before serving and you won't need a steak knife. In fact, you should never need a steak knife; they were invented to disguise mediocre badly cooked steak. A meat thermometer is most accurate for testing thick fillet; 50C for rare or 60C for medium-rare.