This series is about a witch who lives in an old house that’s been turned into a tearoom. At first, she tries to scare the new owners of the place away when they buy the old house she haunts and start fixing it up as a tearoom, but she makes friends with the boy in the family, and they come to appreciate her cooking skills.
The old witch in the stories doesn’t really have a name. She’s just called the Old Black Witch (because of the black clothes she wears) or Old Witch.
The authors, Wende and Harry Devlin, also wrote a number of other children’s books and series, including the Cranberry Books.
Books in the Series:

Old Black Witch (1963)
A witch who haunts an old house is horrified when someone buys it to turn it into a tearoom, but they end up becoming friends.
Old Witch and the Polka Dot Ribbon (1970)
Old Witch enters a baking contest at a carnival.
Old Witch Rescues Halloween (1972)
When the celebration of Halloween is banned, Old Witch comes to the rescue!