Meat thermometer.
60°C/140° F - rare
70°C/160F - medium
80°C/175 °F - well done
The problem with instructions like ' x mins @y temp per lb/kg' are only guidlines as cooking times and accuracy of temperature varies oven to oven.
Each to their own Mark. Personally I don't use a thermometer for beef, only for large turkeys and pork joints. I like to know these are cooked through without being overdone.
However if you are unsure the safest, easiest, least likely to foul up way of checking would be with a thermometer. I have enough skills to be able to judge how long a piece of beef needs, to be to my liking, depending on size and cut and cooked in my oven and also have my own personal ways of checking this. Others perhaps are not so confident as you and I.
Slow roasted a nice fore-rib last week. It almost melted in my mouth![]()
Leave it out for an hour to get to room temperature .........
Love a fore rib, my all-time favourite. Nice and pink, well rested with some good horseradish and home made yorkie puds, fantastic.
Rare
20mins per 450g/½kg(lb)
+ 20mins
Medium
25mins per 450g/½kg(lb)
+ 25mins
I like to sear mine in the pan on the hob first, after well seasoning with pepper, sea salt and mustard powder. Put in oven at full whack the reduce.
Ovens vary massively, so thermometer is advised, but maybe make a cut in the meat to have a look. Best to rest it for 30 mins minimum, 45-60mins ideal, wrapped in foil then put a tea towel over. Will continue to cook, so take out before it looks done. Worst case is you cut, and its too rare, you can pan fry a bit, or that said, put slices on a hot plate and put hot gravy on and it will be fine.