My late Viennese grandmother's recipe for plum torte, and one of my favorite ways to eat Italian prune plums:
Viennese Plum Torte
1 cup sugar
1/2 cup unsalted butter (aka 4 oz. aka 8 tbsp. aka 1 stick)
1 cup flour
1 tsp. baking powder
pinch of salt
12 prune plums, halved and pitted
Topping: sugar, cinnamon (approx. 1 tsp.), half a lemon (optional)
Preheat oven to 350 degrees. Butter a 9" springform pan (you can also use a pie plate).
Cream sugar and butter in Mixmaster until light and fluffy. Add flour, baking powder, salt, eggs, and mix well.
Pour batter into prepared pan. Place the plum halves in the batter, skin side up. Sprinkle lightly with additional sugar and cinnamon to taste, and squeeze lemon over all the plums (you might not need all the juice).
Bake at 350 degrees for one hour. Remove and cool. Can be refrigerated or frozen. Serve warm or cooled, plain or with vanilla ice cream or freshly whipped cream.