Given your lack of tools, we're going to have to get MacGyver on this roast.
- You'll need some sort of flavorful liquid (or a combination of them). Chicken stock or beef stock would work. I'd normally also recommend using something acidic like red wine or tomatoes, however, using this method (which is based on tinfoil), acids can react with the aluminum to produce off flavors. If you want to cook with wine or tomatoes, you can transfer the meat to your casserole after you brown it. (More on this below.)
- You'll also need some type of mild tasting oil. Vegetable, corn, canola/rapeseed, peanut, light olive oil, will all work.
- Salt.
That's it in terms of software.
Hardware:
- Paper towels.
- Tinfoil (preferably the big, wide kind, and heavy duty).
- An oven.
That's it.
Algorithm:
This is basically the same technique that Cos Callis proposed, just using different tools.
Adjust your oven's rack to about 6 inches from the broiler. Turn on your oven's broiler on its highest setting.
Lay out two layers of tinfoil on your counter. Make sure the tinfoil is big enough such that if you were to place the roast in the middle of it there would be a border of tinfoil around the roast that is at least as wide as the roast itself.
Optional: Put the tinfoil on a large sheetpan or cookie sheet. This will help you in transporting the device to/from the oven, and it will also ensure against spillage in your oven. If you do things right you won't have to wash the sheet.
Pat the meat as dry as you can get it and put it in the center of the tinfoil.
Pour a bit of oil on top of the roast and rub it all over. You only need enough to barely coat the entire roast.
Generously salt both sides of the roast. I prefer using kosher salt, because it is less saline by volume, so you can more evenly distribute it without over-salting. You'll probably use a good tablespoon or so.
Put the roast under the broiler. Wait about 5 minutes, but that number isn't exact. Use your eyes. Just wait until it looks good and brown and crusty and delicious. Just don't blacken the entire thing.
When the top side is browned, flip it over to the other side. The best tool for the job here is a pair of tongs, but a fork will do.
Brown the second side.
Remove the roast (which is hopefully on top of some type of pan for your convenience).
Turn off your broiler and reset your oven to 275 degrees F.
Fold up the sides of the tinfoil around the roast to make a sort of pan around it. Try to leave as little room around the roast as possible.
Alternatively, if you want to use acidic ingredients, you can transfer the roast to the casserole at this point. The reason why you couldn't use your casserole from scratch is that it is probably not broiler-safe.
Pour in enough of the beef/chicken stock to just barely cover the roast. It shouldn't require very much liquid.
Once the liquid is in, fold the tinfoil on itself to seal the top, such that you end up with a tinfoil package containing the browned meat and the stock. Try and make it airtight.
Stick that in the 275 F oven.
Just let it sit in there for ~3 hours. You don't need to touch it.
After ~3 hours, take it out. Hopefully the tinfoil didn't leak.
If you did this correctly, all the cleanup you need to do is crumple
up the foil and throw it out.
You can also experiment with adding other vegetables (e.g., thinly sliced onions or whole garlic cloves). You can even add them from the very beginning.
As I mentioned in a comment on Cos Callis's answer, bottom round roasts have a lot of tough connective tissue which needs to be cooked low and slow (<300F) in the oven in order to become soft and tender. However, if you were to cook the beef the entire way at that temperature the meat would end up being gray and tasteless. The reason is that the Maillard reactions (which are what turn the meat golden brown and make it taste more meaty and delicious) don't really occur below ~300F, which is the purpose of the initial sear.
The common method would be to cook the pasta in advance, then shock it in cold water to stop the cooking before draining and refrigerating it. You would then heat it up in boiling water for about 20 seconds just to heat it through.
You would just need a portable burner to keep a pot of water boiling for service.
On the other hand, 20 pounds of pasta for 200 people is a portion size of only about 1.5 ounces per person. That is a very, very small portion, less than side-dish sized.
For side dishes, 2 ounces of pasta is more typical. If you are serving it as a main dish, 4-5 ounces would be more typical.
(Weights are for dry pasta.)
Best Answer
I think a microwaved, reheated burger is probably not going to compare favorably to a freshly-cooked burger. With that said, I think the main thing for the pre-cooking is that it would need to be start off a little undercooked, otherwise the heating process is going to result in it being overcooked (since you're saying you're looking for some pink in the middle).
Other than that, I think the key is more in how you microwave it. Obviously, you want it to cook evenly. I'm assuming you're starting from refrigerator-cold. If you start from frozen it is going to have a lot more trouble heating evenly. Also, it might go without saying, but I'd cook the meat on its own (no bun or condiments).
Most microwaves tend to have hot spots in certain areas. There is a pretty interesting (IMO) blog post that demonstrates this using papadam (those crispy lentil crackers you get at many Indian restaurants). The ones tested in that experiment, seemed to mostly be good directly in the center of the tray, so that might be the best placement. If you want to be really super-scientific about it, you can try to replicate that method and figure out how to arrange your food in your microwave.
But if you don't have any papadam handy and you don't know what your office microwave is doing, you may want to find a supposedly-microwave-safe plate that still tends to get hot in the microwave and heat your burger on that. I think the plate is going to transfer heat more evenly to the burger than the microwave would. (On the other hand, I sometimes question whether dishes that get really super hot in the microwave are, indeed, as microwave-safe as they claim to be, so use caution....) Using a real plate, though, instead of a paper plate should help with the evenness of the heating.
I'd also suggest cooking it in short bursts (15s at a time) and letting it rest in between, or cooking it on low if your microwave has power settings (which just does the same intermittent power thing anyway).