Hi,
I had some spare time in Phnom Penh & decided to do a cooking class. The one I chose was Cooking Cambodian (www.cookingcambodia.com). I was able to book at my guest house (saved me some trouble). It turned out to be a good choice - I was collected from my guest house & had a great day (they even brought me back afterwards). I chose to do the full day course. The chefs were great, really patient with someone who can easliy burn water! All in all a great day - cannot recommend it highly enough. Make sure you include this in your trip to Phnom Penh.