Method

1. Preheat oven to 200°C / 180°C for fan assisted/ Gas M. 6
2. Cook the potatoes in boiling salted water for approximately 10 mins or until just tender, drain well and cool.
3. Unroll the pastry sheet and cut it into 4 equal rectangles, place on a lined baking sheet and spread each with wholegrain mustard.
4. Divide the leeks and potato between the pastry leaving a border.
5. Brush borders with beaten egg and pinch up around sides to form a wall. Brush again with beaten egg and scatter each tart with grated cheese.
6. Bake for approx. 15 minutes until pastry is golden and cheese melted.