Preheat the oven to 180°c (fan assisted). Line a baking tray with baking paper. Cut the pre rolled puff pastry into 12 10x4cm rectangles and place on the baking tray.

Use a pastry brush to brush the top of the pastry with the beaten egg. Sprinkle lightly with the sugar. Place another piece of baking paper on top covering the pastry rectangles, and a wire rack or lightweight baking tray on top (this is to stop the pastry rising too much). Bake for 25 minutes, or until golden and crisp.

In the meantime, toss the cherries in the sugar and place in a baking dish. Cover with aluminium foil loosely and roast for 10-15 minutes, or until soft but holding their shape.

Remove the cherries and pastry from the oven and set aside to cool. Split the pod in half along the length. Use the back of the knife to scrape out the grains. Add this to the cream in a large bowl. Whip up the cream to soft peaks with the sugar. Beat the soft curd to remove any lumps.

Fold the whipped cream in the curd. Place in a piping bag fitted with a star shaped nozzle. To assemble, place a small blob of mousse on the plate to stick the first pastry rectangle down. Line the cherries up along one side of the rectangle and pipe small dollops of cream along the other side. Repeat the process with the next rectangle. Dust with a little icing sugar. Repeat the whole process another three times to make 4 in total.

Tips
Place a metal bowl in the freezer for 10 minutes before whipping the cream in it. It will make whipping the cream easier.

Get ahead
The pastry rectangles keep in an airtight container for several days. The roasted cherries can be kept in the fridge for up to 3 days.