20 Italian purple plums pitted and quartered 
The pastry
2 C flour
1 C sugar
6 oz.   softened unsalted butter 
1 large egg
1 tsp. pure vanilla 
2 Tb. milk  
Preheat oven to 400°.  Butter and flour 2 8-in. cake or springform pans.
Combine flour and sugar and cut the butter into the flour mixture. 
Combine the egg, milk and vanilla and add to the flower-butter mixture. 
Add extra flower if necessary to make a smooth dough. 
Divide the dough in half and pat each half into the bottom and sides of each pan.  
Place the plums in each pan.  
The custard:
2 egg yolks, beaten 
1 Tb. Milk
4 Tb. sugar  
Combine the 3 ingredients and pour over the plums.  
The streusel:
1 ¼ C flour 
¾ C sugar 
½ C unsalted softened butter 
1 tsp. freshly grated lemon peel  
Combine the above into a crumbly mixture. Scatter over the custard and place the kuchen in the oven.
Bake ten minutes at 400°, reduce heat to 375° and bake an additional 35 to 40 minutes. 
Cool the kuchen on a rack, remove from pans when cool and serve on a cake plate. Ten to twelve servings.  
If serving to smaller number, the second kuchen may be cooled, well wrapped and frozen for later use.