I am looking for two books from the 70’s featuring Merlin the Magician.
A little boy and his dog (Max?) go for a walk in the fog and find a store. The store is actually run by Merlin, who tries to trap the boy. The boy damages Merlin’s hat, which is the source of his power.
The boy and his dog escape, and are later unable to.find the store.
In the sequel, Merlin poses as “Auntie Nilrem” and bakes pies – all the while looking for the boy.
Illustrations were black and white with some pink for Merlin’s clothing.
I hope this helps.