Some good German plum cake recipes are the German plum cake recipe from AllRecipes.com and Zwetschgendatschi, a traditional dessert. Zwetschgendatschi has a thick, cakey crust with Damson prune plums as filling sprinkled with raw sugar.
To make Zwetschgendatschi, blend 1 cup of all-purpose flour, 1/2 cup of cornstarch, 1/4 cup of sugar and 1/2 teaspoon of salt in a food processor, and add 3/4 cup of cold unsalted butter. Blend the ingredients until the dough has a crumbly texture. In a separate bowl, beat together 1 egg yolk, 1 1/2 tablespoons of sweetened condensed milk and 1 teaspoon of vanilla extract. Slowly blend the wet ingredients into the flour mixture until everything is just combined. Knead the dough for a few minutes, and chill it for 30 minutes before pressing it into the bottom of a tart pan. Reserve a little of the dough for later.
Cut 3 pounds of Damson prune plums in half, and arrange them on the crust with the skin side down. Sprinkle them with raw sugar and the reserved tart dough. Bake the cake at 350 degrees Fahrenheit for 45 minutes.
Make another plum cake recipe by creaming together 1 cup of sugar and 1/4 cup of softened butter and beating in 2 eggs. Combine 2 cups of flour and 2 teaspoons of baking powder in a separate bowl, and combine the wet and dry ingredients. Pour the batter into a baking dish, and top with 25 halved plums. Make the crumble topping by combining 2 cups of brown sugar and 2 cups of flour and cutting in 1/2 cup of cold butter. Sprinkle the topping over the plums, and bake the cake at 350 degrees for 90 minutes.