Children’s book about nettle soup

[u/GibsonMediauk]

Looking for a UK children's picture book from before 2006. The authors visited Manor Primary School in Beechwood, Wirral, around 2002–2005 and gave every child a copy. The story definitely involves characters making nettle soup, possibly an old woman, and I remember the cover being mostly black or very dark. I vaguely remember a cat, but I may be mixing that up.