Comment on “Druids & Alchemy”

I'm curious: suppose a player worked his druid up to the proper rank of Alchemy and elected to know how to make portable holes. What would your thought process be for figuring out how to make that "recipe," or a similar one, be a satisfying answer for the player? In my view, the player has spent a large amount of resource to gain this knowledge and the recipe shouldn't be so difficult as for the knowledge to be useless (with the world in question determining what "difficult" means, of course. On the other hand, I do agree that the way you do it here (giving knowledge, not some kind of "portable-hole EZ-maker" ability to simply be activated whenever the ingredients are gathered.)