I'm pretty sure you need to use an image mask. This is an image containing only a black shape (a star in your case) on a white background. See a tutorial on how to do this here: http://iosdevelopertips.com/cocoa/how-to-mask-an-image.html
In this scenario, the UIImageView would need to be on top of the UIView then masked using the method in the above link. As far as I know, there isn't a simple way of 'cutting' a shape from a view but this method should give you the same effect.
Another option if you want more control over the shape at runtime is to draw a star as a CGShape and use that as your mask.