the Red Khaganate's very nice page on food.
General remarks: Dairy figured prominently, as did lamb. Vegetables are almost entirely absent (exceptions being onions and garlic, I presume wild versions). Grain products (rice, millet, flour) would have been acquired via trading or raiding. There is little information on medieval Mongol cooking. However, rice cooked in milk and boiled meat served with salt water for dipping are found in at least a few references. I have not seen strong evidence for buuz (the dumplings of modern day Mongolia) but I think that they are an extremely plausible period food. The quantities given here (for buuz and rice, specifically) would serve about four -- I made lots so I would have leftovers. (My coworkers are always facinated by my lunches!)
See previous entry for details on buuz.
The cheese, meant to recreate the "fresh curds" mentioned in several sources, is whole milk brought to a gentle boil and curdled via addition of sour cream. Drain off the whey by straining through a cloth. Salt.
The meat was simply lamb (I used what was cheap at the meat counter, which happened to be blade steak), boiled. I did not boil it long enough. Boiled meat should be served separate from the broth, with a bowl of salt water for dipping. This is actually a pretty tasty way to eat meat, and I will probably do it again. However, I have decided to completely revise my view of this dish and instead do it like (duh, this seems obvious now) shabu-shabu or Mongolian hot pot -- small slices of meat cooked rapidly in boiling liquid. And for the record, I know that modern hot pot is not Mongolian. But I think that the approach (quickly cooking little bits rather than boiling larger hunks for a long time) seems like a good one.
For the rice, I combined 2 cups of short grain rice with 4 cups of milk, brought it to a boil, covered, lowered the heat (to medium, then later to low) and simmered for 20 minutes (15 may be sufficient). When it was done I added salt. I hate rice pudding, so I deliberately avoided having a mushy end product.
Remarks: This was a tasty dinner! My next foray into Mongolian historical cooking, though, will definitely be to re-read period references to the boiled meat feasts of the Mongols as a precursor to hot pot and see if this seems like a reasonable cooking method. I've never had hot pot, but I loooooooooooooove shabu-shabu. In fact just thinking about it has gotten me hungry...