THE MUSHROOMS ARE A REPRESENTATION OF BOTH HOW MUCH DUSK WANTS TO PROTECT/CARE FOR A PERSON AND HOW MUCH COMFORT HE FINDS IN THEIR COMPANY which is why Konatsu had a whole separate room just for his mushrooms. THEY'RE MUSHROOMS BECAUSE HE HAD TO COLLECT MUSHROOMS TO HELP CURE HIS MOTHER'S ILLNESS!!

Also yes it is a horrible cookbook of things he thinks Konatsu might like.