I in particular am interested in the vitamin K2, which comes almost exclusively from organ meats. If I had to bet on one nutrient that’ll get the “duh you should’ve been eating X” in a century or two, it’d be K2.

Thanks for the heads up. Clicky: https://en.wikipedia.org/wiki/Vitamin_K2

\piqued. Very high nutritional density, but these days everyone prefers lean muscle meat, and are put off by organ meats (sadly, myself included). People used to eat them routinely, e.g.: lambs fry, steak and kidney pie, lamb's brains, tripe (lungs), heart.

Tripe isn't lung, but stomach.

As an aside: if you ever visit the Balkans (including Hungary and Romania), definitely try Tripe Soup. It's a local delicacy and it's fantastic.

Tripe is stomach. Lung is not always consumed, but is sometimes. Scottish haggis and related scandi dishes are made from "the pluck" which means lungs, liver/fry and tongue.

Liver in particular used to be something of a comfort food staple in at least parts of the US. I'd encourage people to use fresh veal liver if available rather than the frozen beef liver that may be in the back of a freezer in a supermarket somewhere.

I also like veal kidneys and sweetbreads but rarely see them.

One way to try sweetbread is to see if your local Mexican market with a food court has "mollejas" tacos.

Otherwise I have no idea how the average American will encounter it. Seems super old timey.

I also love buying those large packs of chicken hearts and browning/carmelizing them in a pan.

Every now and then you'll see them on a restaurant menu and you can sometimes get them from a butcher (although TBH they're probably more prep work than is worth it for me). But, yeah, pretty hard to come by.