Which witch? - eva ibbotson

When handsome Arriman the Awful announces a contest to choose his bride, every witch in town is a flutter because only the meanest witch in town will wed Arriman.

Belladonna is dismayed because all she can conjure up are begonias and baby birds.

Illustrations.

When Arriman the Awful, the handsome wizard of the North, announces a contest to choose his bride, every witch in town is a flutter.

The meanest, most powerful witch will wed the wizard.

But little Belladonna is dismayed, because as hard as she tries, her spells conjure up begonias and baby birds, and not a single viper or bloodshot eyeball.

She just has to do something seriously sinister in time for the contest.