The two cases this solution generalizes are the vertical and radial cut method, which both aim towards a single point (you can think of the vertical method as a

The two cases this solution generalizes are the vertical and radial cut method, which both aim towards a single point (you can think of the vertical method as aiming to a point infinitely far beneath the center of the onion). There may be other more optimal ways (cutting each layer individually for example), but they are not conducive to an ultimately simple strategy.