1Preheat oven to hot, 200 C. Line a 20- to 30-cm slice pan with baking paper, using one strip for the base and long sides, extending 2 cm over edges.
2Line base of pan with pastry sheets, overlapping by 1 cm. Brush with yolk and press together to join. Trim pastry to fit pan. Brush with remaining yolk and prick all over with a fork. Bake 12 to 15 mins until lightly golden and crisp. Cool.
3Reduce oven to moderate, 180 C. Prepare cake mix following packet instructions (see tip).
4Arrange plums evenly over pastry base, cut-side down. Pour batter over fruit to cover. Scatter with almonds and sugar.
5Bake 30 to 35 mins, until cake springs back when lightly pressed in centre. Cool in pan 10 mins.
6Using overhanging paper, lift slice from pan onto a wire rack to cool completely. Dust with icing sugar and cut into slices to serve.
TIP: For a standard butter cake mix, you will need to add eggs, butter or margarine and milk.
Photo: Rob Shaw/Bauer