Cream the butter and sugar together in a bowl until pale and smooth. Add the almonds and almond essence, then the egg, and mix together until smooth.
Roll out half the pastry thinly on a lightly floured surface and trim to a 25 cm (10 inch) circle using a dinner plate as a guide. Place on a wetted baking sheet, then spread the almond paste over the top, leaving a 2.5 cm (1 inch) border of pastry around the edges. Arrange the plums in a single layer on top. Brush the pastry border with a little beaten egg.
Roll out the remaining pastry thinly and trim to a circle a little larger than the first. Cut 5 or 6 swirly 'S' shapes out of the centre of the pastry, then lift over a rolling pin and position on the almond paste. Press the edges together to seal and trim to neaten if needed. Knock up the edge to separate the pastry layers slightly, then flute (see
Brush the top with beaten egg and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 25– 30 minutes until well risen and golden.
Leave to cool slightly, then dust the top with icing sugar and serve cut into wedges with cream.