yep, they are a picnic food that are considered a staple, in upstate NY.
Basically, you can buy the ingredients all in the little sack, at any farm-stand during the summer. You get a few pounds of baby potatoes (like the size of a baby's fist, generally), and a sack of salt (the size of a small make-up bag), and you're supposed to boil the potatoes in THAT much salt, and then drain, and add a stick of butter (I mean, honestly!)
I picture them (in my memory anyways) all crusted in salt, and just literally living in puddles of butter. The butter and the poatoes are kinda sharing the spotlight -- they are of easily equal importance.
Before I moved out of upstate NY, I didn't realize they were a regional thing, and so, I remember being like, "Oh, who's bringing the salt potatoes?" when my boyfriend's family was discussing a get-together with the other usual suspects (cole slaw, potato salad, fruit salad, grill meat(.
Well, that crap'll kill you, that's for sure. My grandmother had her first heart attack sometime in her late 50s or early 60s. You don't want to imitate these people!
But now you know!