What the heck is mangosteen?

It's delicious and makes an awesome pure white sorbetto.   When I first saw them in the kitchen I had no idea what they were and they don't really look all that edible, but under that dark purple tough skin is a delicate, sweet, tasty white aril perfect for sorbet and gelato. 

They are really hard to come by in the US and they have a very short season when they are available (only about 6 weeks) so the next time you see it at capo get it before it's gone!