I see 2 places in Hanoi that are highly recommended, but I haven't been to either one. You can read the reviews at the Hanoi Expat website.
[url=http://www.hiddenhanoi.com.vn%20]Hidden Hanoi[/url] - A Vietnamese culture center with both language and cooking classes
Hanoi Cooking Centre - Cooking School (Australian run)
I have done quite a bit of research into this. Look at this site:
and specifically here, this is the one I am going to do:
#3 averydka99 has been a member since 27/7/2010. Posts: 12
The Red Bridge one looks good and is cheap, but it's not in Hanoi - it's in Hoi An. In Hanoi , at the two places Daawgon mentioned, you will be paying at least $40 for a 1/2 day course, around $50 if you want to do a market visit.
Koto also runs an evening cookery course on Mondays 6-8.30pm, $35. They have a website but it's not very easy to navigate and I couldn't find anything about the course on there but the contact number is 0437470337. Highway 4 do an evening course as well - www.highway4.com.
I haven't done any - I looked into it when a friend was visiting but decided to do a course in Sapa instead. It was cheaper!
I did the Sapa Rooms one mentioned above. If you already do a bit of asian cooking you won't learn an awful lot (same for most courses I think) but the experience is worth it - the setting is amazing!