What "seasonal" food or snack would you have all year?

I am sat in front of the fire with a cuppa and a good book and a shortbread and I am in heaven. So I ask myself: "Self, why the heck can't we get a decent shortbread after Christmas?" There being no reply I will set about tomorrow on a quest for a good recipe. A sacred quest.

So... Why are certain foods only seasonal?

Ps. Let's not go down the pumpkin spice rabbit hole...