To make childish and 'cute' into sexy and feminine is near impossible. But this is where the pan collar comes in . This look hit me like a ton of bricks when I saw one of my fav ladies in the world, Anna Karina, in the French sci-fi film Alphaville, and even more so when I chose to use the film as inspiration to design a couple of looks for a project at school.
I'm really into the black and white basic, though styling can be tricky. Totally possible (and fun!) to translate into your wardrobe, though. I've picked out a few dresses, tops and coats but there are plenty of places selling just the collar that you can attach to anything you own.
You're probably all crafty enough to even make your own attachable collar but here are a couple less traditional styles you can pick up on a budget :)