The plot as I remember it: A young boy and his mother move into an old house in the country (this could be set in England, not sure). I am unsure about the boy's name, but I believe his name is "Nicky" or something similar, and I don't recall if there was any reason given for his mother being single, such as being a widow, or divorced. They discover a short, frizzy-haired witch who lives in the house and isn't happy about them moving in, but they change her mind and make a cozy space for her in the attic, which she is happy with. She has a signature curse that she uses throughout the story, usually exclaimed at passersby: "rats, bats, and snakes' knees!" The mother starts some business (bakery, perhaps? Not sure) in the house and the witch becomes very helpful. At some point in the story, some burglars break into the house and when the witch confronts them, they put her headfirst into a barrel of flour. As they are pilfering things, she carefully peeks out from under the lid of the barrel and turns them into toads. The story ends happily with the witch enjoying her new pet toads, which she keeps in a small bird cage in her attic room.

I remember reading this book when my family moved into a house formerly owned by some friends of the family, and this book was left behind. I was about 7-8 years old, so it would not have been published later than 1978.  It was hardcover, large format (at least larger than letter or A4 size, and formatted almost square), and not very thick, so it would be a short story. It was very well illustrated, with the witch's character drawn more cartoonishly with very small eyes and a large rounded nose, but everything else was drawn more normal.

It's just one of those things that nags at me in the back of my mind every once in a while and it bugs me that I can't remember the title. Thank you!