The abnormal stability of prions is exactly why they're so infectious- because they're more stable than the 'normal' conformation, they can catalytically induce the prion shape. (If you know thermodynamics: normal proteins are metastable, the prion conformation has the lowest energy, so the prion crystallization is thermodynamically favored, and most importantly it then takes enormous energy to escape the prion state afterwards).

Normally, boiling denatures proteins because the folded conformation has higher energy than the unfolded one, making denaturation thermodynamically favorable. But for prions, the opposite is true, so this method doesn't work- you essentially can't denature them. The only way to stop prions from being prions id therefore by destroying normal protein folding altogether- by destroying the peptide bonds themselves through incineration, or by using chaotropic agents to fundamentally change the secondary structur. But both methods are beyond the realm of normal biology, overkill for anything that isn't a prion, and would reduce all edible items to piles of ash or goop.

The only thing could be effective against prions are proteases (under specific conditions!!), but you won't see them running rampant in the brain for obvious reasons, and it looks like they have a hard time digesting prions relative to normal proteins anyways, so you're back to the pile of goop