What is the best way to remove burnt popcorn from stainless steel pot?

Try a steel wool pad like an SOS or a Brillo pad

steel wool and dawn dish soap followed with some cleanser if there is still any residue.

Warm water, few drops dawn, fabric softener sheep on top, let soak hour or more, dump water, wipe clean. Works for rice, beans and potatoes too.

First put baking soda sprinkled in the pan to cover it. Next add some water just so it covers the burn. Simmer on medium for 20 minutes, watch the pot, so it doesn't dry out. Scrape the burnt on popcorn, and rinse, then finish with SOS. Good Luck!

Try Bon Ami

Hello, hope this helps. Boil water in the pan, and let sit to cool then as soon as you empty the water from the pan, sprinkle in some Barkeepers friend, and scour the pan, rinse and repeat the scour if you missed any spots.