I've been trying to find this book for some time now, I read it some 10-15 years ago in a library so it could be a bit older.. It's more so a fairy tale than actual fantasy but still.
It's the well know story of Hansel and Gretel but told from the perspective of the witch, who in this story is good.
The details have become hazy over time but I especially remember her cutting of her own tongue so she couldn't curse the kids, as well as trick the kids so they would throw her in the fire, preventing her from ever hurting them again.
She was trying to protect the children from some curse put on her or some demon inside of her, something along those lines.
Anytime I try to look for this book I end up with search results on the Hansel and Gretel witch hunter series or some fan fiction book on this subject..
Edit: This is a separate (short) book, not part of some collection of stories or fairy tales