|Left-over fillet steak thinly sliced and served with home-made mustard|
mayonnaise and fresh dill. I like fillet quite pink in the middle, but if you
prefer it medium, leave it in the oven for a little longer.
Even with the aid of a digital cooking thermometer/probe, I've found it difficult to get the same results every time, so now I judge the 'done-ness' of a fillet by touch and instinct, and sometimes by going against all the cheffy rules of cooking and slicing deep into it to check whether it's ready (see below).
So try this:
Three hours before you're going to cook it, take the fillet out of its packaging (strictly speaking, it shouldn't be wrapped in plastic at all, but let's not be precious about this), drain off all bloody liquid, pat it quite dry with a paper towel and put it into a ceramic dish so it can slowly come up to room temperature.
One or two hours before cooking, trim and flavour the fillet. Using a sharp knife, cut through then peel away the 'silverskin' (membrane) on the outside of the meat (good instructions here). Double the thin end over and tie it to the main fillet with string. Don't worry if one end is much thicker than the other (the thick end will cater for those who like their fillet rare, and the thin, doubled-over end will do for those who like brown beef).
Whether you're braaing or frying, preheat the oven to 190°C, and place a metal roasting pan in the oven to heat through.
Immediately before you cook the fillet, put a generous dollop of good prepared mustard (such as Dijon mustard) in the palm of your hand and smooth it all over the fillet. Sprinkle liberally with olive oil and a little salt, and grind over plenty of fresh black pepper. Add any other flavourings that you think might be good (a dash of good soy sauce or a very light dusting of mild curry powder are to be recommended, but don't use fresh garlic, which turns bitter when it browns in hot fat).
If you're frying: Heat one to two tablespoons of olive or sunflower oil in a frying pan over a high flame. Wait until the oil is very hot, and is just beginning to shimmer in the pan (but it should not be so hot that it is smoking). Put the fillet into the pan and cook on one side for about two minutes - without moving or disturbing it - or until it's a rich brown colour. Turn the fillet and brown it on all sides in the same way; this shouldn't take longer than six to eight minutes. This is a smoky business - if there is no smoke in your kitchen, your pan is not hot enough.
Now add a tablespoon or two of butter to the pan and turn the fillet over a few times so it's coated.
(If you're braaing: Make sure your coals are very hot. Put the well-oiled fillet directly onto the grid and brown it all over in the same way; again, this should take about seven to eight minutes.)
Now put the fillet onto the heated roasting pan and bake in the pre-heated oven for 10-25 minutes, depending on the degree of pinkness you want. A slim fillet takes about 10 minutes; a full-size one 15-25.
If you're not sure, cut a deep slit in the underside of the thickest part of the fillet to check for doneness. This will result in the loss of a little juice, but as you're only going to be cooking the meat for a little while longer, the damage will be minimal. If the meat looks unpleasantly raw and bloody on the inside, give it a few minutes longer.
Alternatively, and a somewhat less accurate method: plunge a fork deep into the meat, leave it there while you count to ten, then hold the tines to your upper lip. If they feel very hot - but not so hot that they burn your lip - the beef should be medium rare inside.
Remove from the oven, cover loosely with a piece of clingfilm, foil or kitchen paper, and set aside to rest on a plate 8 minutes.