Our most used cast iron skillet had a tenacious crust of burned-on grease and carbon that had collected over the years, and because the surface of the bottom of the pan was no longer smooth, many foods would stick. Initially I thought the unevenness was the result of corrosion, but no. I took a sturdy stainless steel spatula to it and with quite a bit of elbow grease over a few days managed to scrape off all the crust and get down to the smooth surface underneath. Now anytime anything sticks and the surface isn't perfectly smooth, I use the spatula with a little water and Dawn dishwashing liquid and quickly scrape until it's smooth again (it's easy to feel with the spatula), followed by my normal routine anytime we use the pan: drying the pan with a dishcloth and then by heating it on the stove, wiping the surface with a few drops of olive oil, and leaving the pan on low heat for a few minutes before hanging it back up on the pot rack. Works great!

What stovetop can reach 1465 °C (2669 °F)?

Maybe GP's mention of "boiling salt" does not refer to "table salt" but salt in the more general chemical sense. Perhaps they use Ethylammonium nitrate with a boiling point of 240 C (464 F).

Can you find that at a grocery store?

I usually order it here: https://store.p212121.com/ethylammonium-nitrate/

$111 for 25g. It might be cheaper to buy a new pan.

Boiling water with salt in it works well, and seems likely to be what OP means. Even boiling water works great.

I suspect a degree of sarcasm just wooshed over me.

It wasn’t sarcasm, per se, it was just a joke.

he's obviously talking about boiling salt water.

Any food on a cast iron pan is converted to carbon ash by holding the pan at 750F for a few tens of minutes if you have a functional exhaust fan. This is useful for the most extremely stuck stuff like large amounts of meat mixed with blood. No amount of scraping would get that off. However the ash came off effortlessly. The electric range was old and worn out but got the job done easily.

I found a hoard of old unused sad cast iron pans at my wife’s grandma’s place. Putting them in the electric oven and running a self-clean cycle completely stripped them down to bare metal. From there, they were seasoned from scratch and have been in service for a decade now.

How bad was the smoke

Oh, terrible. Acrid. I’m lucky I did it during the day and my wife wasn’t home.

I put in dry salt and use it as an abrasive (while hot).

It also soaks up any excess fluids.

just get a plastic hard plastic scratch (lodge sells them on amazon) never had any burned on thing not come right off.