Roll out the pastry on a lightly floured surface into a 10 inch (30 cm) by 15 inch ( 37.5 cm) rectangle, about 1/4 inch (5 mm) thick. To ensure that the dough rises evenly and does not buckle during cooking, prick all over with a fork.

Trim the edges, cut into three strips each 5 inches (7.5 cm) wide and place on dampened baking trays. Cover the trays with cling film and refrigerate for 30 minutes. Bake in a hot oven (Mark 7 (220°C) 425°F for 15 to 20 minutes until well risen and golden.

Remove from trays and allow to cool completely on a wire rack — warm pastry would melt the filling. Stack pastry on a chopping board and trim with a large sharp knife.

For the icing, sieve the icing sugar into a bowl to remove any lumps. Make a well in the centre and add 1 tbsp warm water. Stir the mixture carefully, gradually incorporating all the sugar until the icing is smooth and glossy.

Take one of the pastry layers, turn over so the flat side is uppermost. Pour the icing into the centre and spread evenly towards the edges with a palette knife dipped in hot water.

Put the melted chocolate into a small piping bag fitted with a writing nozzle. Pipe straight lines across the width of the wet icing about 1 inch (2.5 cm) apart. With the tip of a sharp knife, drag through the piped chocolate at right angles first in one direction, then in the other in alternate lines to give the classic feathered effect.

Allow the icing to set slightly, then cut into six equal slices using a long sharp knife dipped into hot water before each cut.

To assemble, place first pastry layer on a flat platter and spread with half the raspberry jam and half the whipped cream.

Place a second pastry layer on top and spread with the remaining jam and cream. Place the six iced slices in a layer on top. Chill for 15 to 20 minutes, then cut into six using a long sharp knife and serve immediately.