Bahlsen headquarters in Hannover said the Leibniz cookie, which has been on display outside the facility since 1913, was stolen during the weekend and chairman Werner Behlsen offered a $1,353.90 reward for information leading to its return, The Local.de reported Wednesday.
The Hannoversche Allgemeine Zeitung newspaper said it received a letter Tuesday purporting to be from the thief. The letter was accompanied by a picture of the "Sesame Street" character pretending to take a bite out of the Leibniz cookie.
"I have the biscuit!" the letter reads. "You want it and therefore you want on one day in February, to give biscuits to all the children in Bult hospital. But those with milk chocolate, not those with dark chocolate and not those without chocolate. And a golden biscuit for the child cancer ward."
The letter demanded the $1,353.90 being offered as a reward be instead donated to the local animal shelter.
"This is serious!" the letter says. "Otherwise it will end up with Oscar [the Grouch] in the dustbin, really!!!"
The company said investigators are working to verify the letter is genuine.