Photo: © MrVertigo - Fotolia.com Zwetschgen (Italian Prune Plum) The Zwetschgen (known in the U.S. as the Italian Prune Plum or Empress Plum) is a European-style plum, which is egg-shaped, small and dense, and has a blue and/or purple skin. These plums have a yellow flesh and freestone pits, meaning the pits separate easily from the flesh. The Zwetschgen is particularly good for baking because it holds its shape yet provides plenty of moisture. Also, its has a tartness that goes well with a sweet dough and topping. The Zwetschgen season is very brief - from late August through September.