This German Jewish tart is enjoyed for Rosh Hashanah, when sweet things are eaten for a sweet New Year. In Southern Germany the plums were ripening during the time of the New Year celebrations, and so this tart evolved as a seasonal treat.
Sift the flour into a mixing bowl. Dice the butter and rub in until the mixture resembles fine breadcrumbs. Stir in the sour cream to make a soft dough. Wrap in clear film (plastic wrap) and chill for at least 30 minutes.