I read a Harry Potter fan-fiction a while ago where Harry perfects a sweet potion. I vaguely remember the potion being called "Fairy Floss" or something like that. I'm pretty sure it was either Drarry or at least Slytherin Harry. It was multi-chaptered and pretty long, I think.
The original potion was a children's candy most people above the age of 5 found unbearably sweet and Harry tried to fix it so it was nicer.