What you'll need
- Rosemary (optional)
- Butter (or oil)
- Pepper and salt
What you'll do
Take the lamb fillet or lamb chops out of the fridge and let them heat up a bit. Pat them dry with a paper towel and coat both sides with salt and pepper.
Pre-heat the oven to 200° C. Also place a cast iron skillet on medium-high heat and add in some oil or some butter (please do not burn the butter. If the butter is brown you need to throw it away, lower the heat, and restart).
Place the lamb in the skillet with rosemary (if you want) and sprinkle with thyme. For a 2cm thick cut you want to sear it 2-3 minutes per side. You could finish cooking the meat on the flame, but that will make it less juicy. If you want to go down this road, you'll need about 8 minutes additional cooking per side on medium heat, and baste it with a knob of butter every few minutes. Internal temperature should be around 140 for medium-rare, and 160 for well done.
What I recommend, however, is to finish it in the oven. 14 minutes for medium, and you're good to go. Then take it out of the oven, let it rest for a few minutes (it is still cooking...) and serve!
It's really good with roast potatoes.