Preheat oven to 170C. Grease and line a medium round pan.
Mix together 1 2/3 cups flour, 1/4 cup Natvia, baking powder, 1/3 cup butter, and the eggs in a bowl. Mix with a spoon until well combined.
Transfer to the pan. Line the dough over bottom and sides of pan. Followed by adding the plums.
Combine the remaining flour, Natvia, cinnamon, and nutmeg together in a separate bowl. Add the 1/2 cup cold butter and mix with hands. Sprinkle the crumb evenly over the plums.
Bake cake for 40 minutes or until golden brown.
Cool on a wire rack. Serve in slices or straight from the pan.
Optionally you can add cream, enjoy while still warm!