what is the best way to roast beef to serve sliced as part of a cold buffet?
Cold roast beef rarely does the meat any favors (there's a reason it rarely shows up on charcuterie plates), but the best way to roast beef, is the best way to roast beef whether you serve it hot or cold.
Particularly since you are going to be serving the beef cold, consider dry-aging the cut for a couple of days in the fridge to concentrate the beefy-ness of it. Then all you need to do is season it with a good rub down of salt and pepper (some oil will help it stick). Bring the meat to room temperature, then roast it slow and low to below desired internal temperature. A good med-rare is about 130ºF, but the carry-over of a large hunk of meat can be significant. Let your meat rest while you crank up the oven to high-heat, then roast it for another 15 minutes or so to develop the nice crust.
You can let it cool completely before slicing, and serve with some flavor-packed sauce: horseradish is traditional, but I've had some interesting Asain-inspired "jellies" which bring a different flavor profile to the dish.
PhillipBrandon, I am curious about your suggestion to roast at high heat after resting. Will that not negate the redistribution of juices that's just been accomplished by resting, or is 15 minutes not enough time for that to happen? Does this idea of cooking THEN browning, as opposed to the other way around, have to do with the size of the meat?
I have to admit I'm a little skeptical about the second roast myself but I'll look forward to seeing the answer. I agree that 130F is the right time to pull it out and tent it. For that crust I think it's better to start it in hotter oven, like 450F and then drop it down.
Browning at the beginning hasn't ever made much sense to me. It takes a lot longer because of all the water that would otherwise have evaporated during a long roast. Since your meat is cooking from the outside in, high temps early on contribute to the brown ring of tough, well-done meat developing around the center. Some people like that, but I definitely don't. I prefer the tender pink center to directly abut the browned crust.
Since the second, hot roast is so quick (15 minutes is really the long end) it doesn't affect the rested meat and juices within very much at all. Though not relevant to the OP, I also like this method because it helps timing a for the rest of a meal or for guests. If you tent, you can stall before the second roast for an hour or so if necessary, just reserve the last few minutes to brown up the outside.
Coincidentally, the whole concept: browning the outside, after slowly and precisely cooking the inside just right, seems to the same that has been adopted by the sous vide movement.
I'll have to experiment with this myself. I know what you are saying about the ring of well done meat around the middle. I'll give your method a shot, I would love to be able to have tender pink meat directly below the outter crust, and if this works, I'll be very happy.
PhillipBrandon, thank you for your clarification. I have to say though that I remain a deep skeptic of the sous vide philosophy.
Thank you for your help and answer. I will let you ok now how this slow cook brown later method turns out. I have a number of sauces on the side including an onion chilli jam. How low should the oven be for the long roast?
Glad to hear it, onion jam sounds fantastic.
Go as low as 200ºF for the low roast. It's best if you have a probe thermometer that can stay in place for the whole time, so you aren't opening and closing and losing heat. Leaving it in the whole time also means you won't have a hole for juices to gush pour out.