Off the top of my head, there are Sarah Rees Brennan, Claudia Gray and Cassandra Clare. I'm sure there must be so many more, though.

[...] as I am so spoiled by fanfic actually giving me all the tropes and kinks I like exactly as I like them.

This is a problem I've been having while reading pro-fic recently; I often find myself thinking, "I've seen this trope handled better in fanfic." I'm so glad someone thought to make a list of fanfic-writers-turned-pro!