This apparently used to be a festively-shaped Crimbo cookie, but it's no longer at all clear what it was supposed to be shaped like, since it got melted by some source of extreme heat. Interestingly, the glaze on it has hardened into actual glass.
A glass of goat's milk is not consumed by eating the cookie with one in your inventory.
References
The glass coating on the cookie may be a reference to Trinitite, the glassy residue left on the desert floor after the Trinity nuclear bomb test July 16, 1945 near Alamogordo, New Mexico.
