I have a pork fillet which I've cut in half and marinated in some honey and soy. I heated a pan, and seared it on all sides, then put the pan in the oven at 180 deg C. The question is, how long to leave it in the oven until it's cooked through? I suspect it's about 20 minutes for the average fillet (3-4cm in diameter). Any suggestions?
Every Kitchen needs a meat thermometer. Little too late in this case but it would have saved you here. I never used one at home until after I started working in a restaurant that only had a flat top and a convection oven with burgers on the menu. I got a relatively cheap one for $5-10 at Wal-mart and it does the job. Another option for next time is to check your meat often and poke it with a spoon, once it feels firm throughout, like the skin on the back of your hand when you make a fist, it's done.
Well, I can report that for this particular fillet, 20 minutes was probably a tad to long. It was a little dry, not overly so, but I think perhaps 15-18 minutes would have been better. However, without an accurate thermometer in the oven or a meat thermometer, it's not a particularly reproducible scientific experiment.
The meat 'is ready' when certain temperature inside it is reached. For pork it's about 82C. The warming-up speed mostly depends on how much fat is there in your meat.
If you have fatty meat it'll be ready very soon, 10-12 minutes maximum or even earlier. If it's lean then the time is a few minutes longer. But in this case it's really worth to take the meat out of the fridge 1-2 hours before cooking and let it warm-up a little bit. Otherwise it's difficult to make it ready inside and not to carbonize the surface.