A site says this recipe drops from one of the Mistborn bosses in Smugglers Pass. I’ve killed him a few times with no recipe drop. Are recipe drops a chance on kill or are they supposed to be guarantee drops?
I think it can drop from any troll boss though I may be wrong on that, he’s certainly the easiest to farm. It’s a chance on kill and afaik he won’t drop it if you are way ahead of him in levels. Sadly it may take you awhile 
Voldrak the Destroyer troll has a chance in dropping the recipe.
Thank you.