Some people learned the Ambrosia recipe by watching the cooking channel. But, I won't recommend it, because it takes a lot of time and you have to know all the other recipes so the only one left is Ambrosia. Really, just save up money (and with Bookshop Bargainer LTR Ambrosia recipe costs only 6,000 simoleons) and get it from the bookstore. That's what I do.