Back-cutting kerfs is one of several ways to do something like this. It wouldn't have worked with this moulding though because of the rabbeted profile on top of the board. The best solution, I think, would have been steaming the board in two or three passes with three jigs of decreasing radius. That was a lot more involved than I wanted to get though so I used a barrel stave approach.

Building up layers of veneers will also work so long as the board doesn't have a face profile and you don't see the edge.