In a small saucepan, combine the sugar and water and bring to a boil without stirring. Over high heat, cook until amber-colored caramel forms, approx 5 to 7 minutes.
Turn off from the heat and whisk in the butter & dry ginger powder. Pour the caramel into a 9-inch round cake pan. Arrange the plum wedges in the caramel in concentric circles. Set aside.
Put all the ingredients of the cake in a mixing bowl and mix using a hand blender, till it is smooth.
Pour over the plums and bake at 180C for 35-40 mins till the skewer comes out clean.
Wait for 20 minutes and then invert the cake on a plate to de-pan. Serve warm or cold. Cake lasts about 2-3 days in airtight container.