My mother used to make the most delicious Plum Cake. Unfortunately I couldn't remember her recipe, but I found one a few years ago in "Heartland Baking" that is pretty close to my mother's Plum Cake.
2/3 cup butter or margarine, at room temperature
2/3 cup sugar
4 eggs, at room temperature
1 1/2 tsps vanilla extract
1 1/4 cups flour
1 tsp baking powder
1 1/2 lbs of purple plums, pitted and cut into halves
For the topping:
1 cup flour
2/3 cup brown sugar, firmly packed
1 1/2 tsps cinnamon
6 tablespoons of butter, cut into pieces
Preheat oven to 350. For the topping, combine the flour, sugar and cinnamon and add the butter with a pastry blender, until mixture resembles coarse crumbs. Set aside. Line a 9-inch round or square pan with wax paper and grease. Cream the butter or margarine with the sugar until light and fluffy. Add the eggs, one at a time. Stir in the vanilla. In a bowl, sift the flour with the baking powder and fold into the butter mixture. Pour the batter into the pan. Cut the plums into half once more and layer the plums on top of the batter. Sprinkle the Streusel topping over the plums. Bake approximately 45 minutes, or until done. Let cake cool down, and then serve slightly warm. It is also good the next day with your morning coffee.