The open-faced sandwich is a simple concept. It's pretty much just a normal sandwich that omits the top slice of bread. It's not groundbreaking. It's not revolutionary. But it's really, really good.
Why is it so much better than a regular sandwich? Well, think about it: the best part of the sandwich is almost always the filling. And when you have an open-faced sandwich, the filling-to-bread ratio is twice as high. This sandwich design is genius in its simplicty. And we have the Danish to thank for it.