One hears around the Périgord:
Nothing is lost in the walnut except the noise when it is cracked!

Indeed the shells are ground up and used for fuel.

A «digestif» is made from the tender walnut leaves by infusing them with old red wine, sugar and some marc.

Another drink is made by macerating fresh walnuts in 90 proof eau de vie.

And of course the walnuts themselves are used in salads, cakes, sweets…