Yay, I finished the game, I really liked it, especially the humour and jokes! The keyboard input for fine-tuning resources added into the cauldron is helpful.
Some minor things I noticed is that at the start of the game without upgrades, it can take a while to transfer resources (so I would open the interface back up, and it would not let me add any more until the animation played out.) It would be nice if the button said "Transferring..." or "Adding..." to explain why it can't be clicked. I also was a bit confused when trying to "queue up" multiple fairies and having resources left in the cauldron, until I realised that this button wouldn't actually add the correctly updated cost until the first fairy had been crafted, but I'm not sure how to fix that in an obvious way. Maybe this interface could predict the correctly scaled cost if you try to add multiple fairies all at once?