There's a great question here: How to add Web API to an existing ASP.NET MVC 4 Web Application project?
Unfortunately, it wasn't enough to solve my problem. I've tried twice to be sure I haven't done anything wrong. I right clicked on "Controllers" and added the item "Web API 2 Controller with actions, using Entity Framework" where I selected my model class and db context. Everything went fine… but still… everytime I've tried to access /api/Rest I was getting a 404 error (The name of my Controller is RestController).