Siretoco Factory Ecute Ueno
Time Out says
Hokkaido's Nakashibetsu Town is the birthplace of the Shiretoko Doughnut, named after the peninsula that's known as one of the most remote regions in all of Japan. Made with milk from that same region, these goodies are soft, sweet and cutesy, especially when made in the adorable panda shape sold at this Ueno location. Flavours range from milk and caramel to pumpkin and chocolate, so you might want to buy more than one while you're at it.
Inside Ecute Ueno (JR Ueno Station 3F), 7-1-1 Ueno, Taito-ku, Tokyo