Try the Institute for Culinary Education. They have one-day and week-long courses. They have some beginner courses, but most people in the room have some background, so even the beginner classes are meaty. They also offer advanced classes. I have taken a few and you will find lots of hobbyists, part-time cake decorators or people who work in bakeries that want to advance their cake decorating skills. The instructors are very good (toba Garrett teaches many classes and heads up the program) and they use top quality ingredients and equipment. I think their prices are very reasonable and they offer the most classes of anyone else I've seen.
You could also try the French Culinary Institute but they have fewer classes and are twice as expensive.