1.Preheat oven to 180°C (160°C fan-forced). Grease a 24cm springform cake pan; line base and side with baking paper.
2.Sift the flour, baking powder, ginger, cocoa and salt into a large bowl. Beat the butter and brown sugar in a medium bowl with an electric mixer until light and creamy. Beat in eggs, one at a time. Stir in sifted dry ingredients and buttermilk in two batches.
3.Pour batter into prepared pan. Arrange plum pieces on top, cut side up. Sprinkle with the cinnamon and coconut sugar.
4.Bake cake for about 50 minutes or until a skewer inserted into the centre (not through a piece of fruit) comes out clean. Cool cake in pan.
5.Dust cake with sifted icing sugar and serve with thick or whipped cream, if you like.
If coconut sugar is unavailable, use demerara or raw caster sugar. Suitable to freeze. Not suitable to microwave.Note