Leave the puff pastry to defrost and cut a line across the edges of about 1 cm wide. Don't cut all the way through the pastry. Brush the edge with the whisked egg and prick holes with a fork in the middle.
Generously spread the boursin in the middle. Press the asparagus into the cheese and add the tomatoes in randomly.
Put into the oven for about 15-20 minutes or until golden brown and the pastry cooked