Young nuts are eaten together with their shells because they are soft and edible. What is the brocha on such a food?
jutky was on the right path.
An adult nut in its' shell - Ha-aytz
A young nut in its shell- If the nut is usually eaten unripe, then it would be a Ha-aytz, because this is considered the normal way to eat the "fruit". However, if the nut is not usually eaten unripe, then the nut is not yet a fruit, so the brocha is Ha-adamah.
Shells and peels that the fruit can live without and are eaten alone (eg. caper shell)- Ha-adamah peels that the fruit would die without and are not normally eaten (eg. orange peel)- Shehakol
mostly Bruchos 36a+b (ripe fruit is in Beruchos somewhere, but I can't find it)
If it is way of eating nuts (דרך אכילה) then it should be "פרי העץ".
Or do you want to eat the shell without the nut itself?