I have a new group of 3, they all made a bit of a back story and one of the three have made an exceptional background story.  He goes on to explain details of his life at specific ages and what happens up til the beginning of this campaign (I've been a DM for 10+ years now).  I've seen all sorts of backgrounds, small and big, until this guy.

Without going into a lot of detail, I can if you like, this Half-Elf Ranger has a specific food item he goes particularly crazy about.  To the point if he sees anyone eat it he will go out of his way (good or bad) and do anything he HAS to do in order to obtain it, hoards it and then consumes it in a horrifying manner... every time.

I was talking with him today about it and he wants to pick a fruit or vegetable, this has to do partly with his background bio, but it needs to be something that's not in abundance.  We aren't talking only three of its kinda out there, but more along the lines of very hard to obtain (illegal maybe?) or Super Rare that anyone would break the law for its value or prestige.

Now... For the life of me I cannot think of anything that would be suitable, is there anything that's this rate in the  D&D world or should I Homebrew this option??

Any help will be great and thanks for taking the time to read this, if you want the biography let me know.

I don't have my books around me, but there have been modules set in places where there are rare fruits, Gulthias tree has something like this. The problem is those fruits are of the "once a year" type thing. I would suggest coming up with something, homebrewing it and really giving it some (incoming pun) flavor.

Durian is a great example of this. An amazingly strong smell, has an esteemed place in the local area it grows, and is extremely hard to get as many places have banned it. This make it something that people will seek out due to the mysterious and difficult to obtain nature it has. 

Before modern transportation dishes used by nobility to display their richness and prestige often included foods from far away, especially when keeping it fresh would be difficult.

Think of fresh oysters from the sea, served still alive in the shell 700 miles inland.

So you could pick a fruit or vegetable that you just declare is not ingegenous to the region. Pineapple, mangoes, starfuit. Whatever it is grows far away and must be specially preserved in order to make it this far without going bad.

Alternatively, a fantasy veggie, say Faerie Circle mushrooms. Illegal and hard to find as local custom demands such circles be destroyed whenever found.

A specific tuber (golden yam) or mushroom (truffle) which only grows on the elemental plane of Earth. It is farmed or harvested there by the Dao (well, by their slaves). Then every now and then some of these treats are traded to mortals, usually as part of a slave deal. Thus the vegetable is rare, not inherently illegal, but also almost never moral to acquire. Ranger's unattainable dream is to defeat a Dao Kingdom and free the slaves - but then hire them immediately to work on his farms where he can finally experiment with every way to cook or prepare the food. Perhaps the ranger develops an obsession with tracking down slavers and destroying them, but in truth that is just because maybe they have some clues leading to more treats. 

It would be better if he had some kind of personal vow to not eat the same thing twice. So everything he eats has to somehow be different than the time before. Then YOU don't have to worry about anything specific, and HE has to track what he's eaten.

One of my PCs is a foreign noble of an island nation. I have planned that the primary export of their nation is a type of molasses sugar that is made from the sap of trees that only grows on those islands.

My point being, sugar is more of a luxury item in a medieval setting.

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A specific tuber (golden yam) or mushroom (truffle) which only grows on the elemental plane of Earth. It is farmed or harvested there by the Dao (well, by their slaves). Then every now and then some of these treats are traded to mortals, usually as part of a slave deal. Thus the vegetable is rare, not inherently illegal, but also almost never moral to acquire. Ranger's unattainable dream is to defeat a Dao Kingdom and free the slaves - but then hire them immediately to work on his farms where he can finally experiment with every way to cook or prepare the food. Perhaps the ranger develops an obsession with tracking down slavers and destroying them, but in truth that is just because maybe they have some clues leading to more treats. 

I like the way you think, the player is always coming up with ideas and thoughts.  He does have a few social anxieties and other issues we've discussed and since he's played he has begun to open up more.  D&D has helped my friend in more ways than I could imagine so I want to help by adding more to his story.

Thanks!