Preheat oven to 350 degrees.
Halve, pit and quarter the black plums.
Mix together in a bowl the flour, baking powder, cinnamon, nutmeg and salt and set aside.
In a separate bowl, combine the butter and 1 cup sugar and mix with beaters until well blended, a few minutes.
Add the egg and vanilla and mix until incorporated into the butter mixture.
Add the flour mixture and milk to the butter mixture alternately until a thick batter is formed.
Spread into a prepared 9 inch spring form pan. Arrange the plums on top and sprinkle with 2 teaspoons sugar and bake for 60 minutes.
Remove from oven and allow to cool. Top with the remaining 2 teaspoons sugar and release the springform wall from the cake. Serve and enjoy!