There is a science to roasting meat, even if a successful result seems like pure artistry. I roast quite a lot, and my obsessions are-
- getting the right cut
- getting good quality raw meat
- calculating the cooking time right
- calculating the heat right.
As others have said above, the best roasting cuts will have some fat in them. The fat renders during the cooking process, and keeps the meat moist.
So, pork shoulder is good. Pork loin is bad (and expensive), because it has just about no fat and dries out. Lamb shoulder is good for the same reason, lamb leg less so. Mutton can be fantastic, but it requires careful cooking or it ends up like an old boot.
Buy from a butcher, who can advise you what cut will do best. My butcher sells rolled beef for roasting, silverside I think, but he puts layers of fat in as well, and the results are lovely.
Getting an oven thermometer and a meat thermometer is a good idea: they will help you to know when your meat is done.
Find a table giving meat cuts, weights and recommended cooking times.
Meat on the bone will cook more quickly than meat not on the bone.
Don't roast widdly piddly little pieces of meat: I roast at least 2.5kg at once. You can eat the leftovers during the week like our grandparents did. This is particularly important if you want to get decent crackling (NB - Politixmum, thanks for the tip - I will try that next time to see how it works. I normally score mine and put salt over).
With beef, it's helpful to start at a high temp, ie, 200 degrees, and then reduce: it gives the meat a particularly toothsome smell and flavour.
BTW, can anyone tell the difference between British lamb and NZ lamb?