Roll the pastry out and fold the top third down into the middle then the bottom third back over it. Wrap in cling film and chill for 15 minutes. Repeat this process twice, then roll out the pastry and cut into 10x10cm squares. With a sharp knife, make diagonal cuts from each corner to within 1cm of the centre. Put 1 teaspoon of jam in the centre of each pastry and fold in each corner to the centre. Place another teaspoon of jam in the centre and leave to rise for 30 minutes in a warm place before baking.