How to draw a mesh transparently without "hidden parts"?

Hi everyone,

This question can seems trivial (or I can be a real noob) but I will really appreciate some help on this point.

Take the simple example of a mesh created from a sphere and a cube inside ; the cube is not shown during a normal draw due to default ZTest LEqual. I would like to draw the same thing but with alpha blending (so only see half of the sphere and evertything behind in the scene).

I first imagine that a simple shader with two passes ; one to draw only depth and a second to draw only the material will do the trick but I cannot manage to do it.

Thanks in advance for the answers.