Handkäse (literally: hand cheese) is a German regional sour milk cheese (often Harzer) and is a culinary speciality of Frankfurt. It gets its name from the former way of producing it: forming it with your own hands.
It is a small, translucent, yellow cheese with a pungent aroma that many people find unpleasant. It is sometimes square but more often round in shape.
Often served as an appetiser or as a snack with Apfelwein, it is traditionally topped with chopped onions, locally known as "Handkäse mit Musik" (literally: Handkäse with music) - so called because of the sound of the resulting flatulence. It is usually eaten with Caraway on it (as seen in the first picture). Since many people in Germany do not like this spice, in a lot of areas it is served separated. Lots of Hessians say that it is a sign of quality of the location when you get your caraway in a separate dispenser. As a sign of this, in many restaurants you will find additionally to the salt and pepper a little pot for caraway seeds. Hessians delight in introducing foreigners to this delicacy and explaining the name's provenance.
An alternative theory of explaining "Musik" is that the vinegar and oil flasks were formerly given separately to the guests, and that when they hit each other, they made that sound.