Trying to find the title of a fantasy short story I read in the early 80's. in the opening scene a boy draws a cookie, picks it out of the paper and eats it. He draws a horse in pastels that comes alive and he tries to keep it, by saying "Fixative". I think the boy's name was Jeremy.
A Proper Santa Claus by Anne McCaffrey.
The boy is Jeremy North. The cookie scene is:
He shaped a cookie and put raisins on it, big, plump raisins. He attempted a sugar frosting but the white kind of disappeared into the orange of the cookie. So he globbed up chocolate brown and made an icing. Then he picked the cookie out of the paper and ate it. That left a hole in the center of the paper. It was an excellent cookie, though it made his throat very dry.
The horse scene is:
His mother and grandmother were engrossed in discussing the fixative that would have made the pictures "permanent." Gramma said she hadn't bought it because it would be dangerous for him to breathe the fumes.
The horse went cantering around the room, pink tail streaming out behind him and pink mane flying. "... Fixative, Green Horse!" But it didn't work. Jeremy knew it took more than just wishing to do it proper.