My sweet little friend Anna copied out a bunch of recipes that she thought I should try making. The first one I tried was the one for Lemon Drops. Since I don't know what her exact source was, I'm not going to print it out here, but honestly, it's the same recipe that I see for lemon drops everywhere!
I'm betting that Anna has a book similar to this one:
The Unofficial Harry Potter Cookbook: From Cauldron Cakes to Knickerbocker Glory--More Than 150 Magical Recipes for Muggles and Wizards by Dinah Bucholz