My favorite donut is the Bismarck. They are sold in grocery stores in Northern Iowa. I thought I would post a photo because, believe it or not, they don't sell these everywhere. You might find an imitation but it won't be called a Bismarck. The one I ate today had yellow icing piped on it, which is not typical. Usually you just have the white frosting.
A Bismarck is actually based on a donut called the Berliner. Berliners are traditionally eaten to celebrate on New Year's Eve (Silvester) as well as the carnival holidays (Shrove Tuesday). A common practical joke is to secretly fill some Berliners with mustard instead of jam and serve them together with regular Berliners without telling anyone.