Curse in Reverse

What's a curse when it's a curse in reverse? If it's a curse in reverse, and it's given by a witch, then it's a blessing of course! When a kindly couple, who long for a child of their own, provide an old witch with shelter one cold night, they are distraught when the witch rewards their generosity with something called "The Curse of the One-armed Man" as thanks the next morning. However, the "curse" turns out to be just what they've been hoping for in this surprising Brothers Grimm-like folktale that is anything but grim!