Take her out for a walk somewhere nice like the beach or a public park.
Then start talking to her and be honest, sincere and let your words come from the heart.
Review in this talk your relationship and be pathetically honest. Tell her about how you used to be someone non-committal(that's better than saying you your just out looking for hook ups all the time) but that after becoming friends with her something changed. She provoked feelings in you you haven't had before and that you would like to explore having a relationship built on more than just friendship, something beyond just a physical relationship, something that's built on trust, friendship, respect, and maybe, eventually love.
Do this and even if she turns you down, at the very least, you will have impressed her as a friend and perhaps planted the seed that grows later on because she knows how truthful, honest, caring and loving a man that you can be.