Another old LanguageHat post concerned Portobello, the large mushrooms that must be the savior of standard American chefs pressed to come up with a vegetarian dish, since they can almost be cooked and served like steaks. The post pretty much left open the question of the word's origin. Another open question of etymology, Pok-a-tok, got resolved by the September 2006 quarterly update to the OED. Remembering this, I checked the December 2006 update and sure enough, they've got it.
Here is the new entry:
ˌpɔːtəˈbɛləʊ/, U.S. / ˌpɔrdəˈbɛloʊ/ Forms: 19- portabella, 19- portabello, 19- portobello. [Perh. alteration of Italian pratarolo meadow mushroom.]
More fully portobello mushroom. A large brown variety of the common edible mushroom, having an open flat cap and a distinctive musky smell.
1990Doylestown (Pennsylvania) Intelligencer 28 Oct. C12/3 Out of darkness now emerge the cream-colored and fuller flavoured crimani..the wild tasting portobello and the soft-for-soup oyster mushroom. 1998Scotl. on Sunday (Nexis) 26 July 32 Before grilling, stuff meaty Portabello mushrooms with oil-soaked crumbs and grated Parmesan or crumbled goat's cheese. 2004Phytochemistry 65 671/2 Tyrosinase, laccase, and peroxidase were detected in portabella mushrooms, a brown strain of Agaricus bisporus.
All we need to do is keep finding mysteries in alphabetical order starting in the middle of the alphabet.
I have to say that even though the earlier discussion did deal with how surprisingly recent this word is, I am amazed that the earliest quotation they could come up with is from 1990. Of course, I don't have any documents at hand that show it earlier, so it must be one of those standard memory tricks.