METHOD:
Preheat oven to 180°C/350°F. Grease a deep 22cm (9-inch) springform pan; line base and side with baking paper.
Beat butter and sugar in a medium bowl with an electric mixer until light and fluffy. Beat in eggs, one at a time. Transfer mixture to a large bowl; fold in sifted flours and milk, in two batches. Spread mixture into pan.
To make spiced crumble topping, blend or process ingredients until combined.
Halve plums; discard seeds. Place plums and blueberries on cake mixture. Sprinkle crumble topping over fruit.
Bake cake about 1½ hours (cover cake with foil if browning too quickly). Stand in pan 10 minutes; remove from pan, transfer to a wire rack to cool.
Serve cake, warm or at room temperature, dusted with sifted icing sugar.