Roll out the pastry on a lightly floured surface in a rectangle to fit an oblong flan tin. Preheat the oven to 180°C.
Place the pastry rectangle over the flan tin and gently press into the bottom and the fluted sides ensuring that no holes are made in the pastry.
Cover with parchment and weight down with baking beans and bake blind for 12 minutes.
For the filling mix the egg with crème fraîche and and season with some salt and pepper. Add the grated cheese, (keeping some back for the top) and chopped ham. Add the potato with the sage and parsley and coarsely mix together.
Place the filling in the middle of the flan and spread evenly to the edges then scatter with the remaining cheese. Place the potato tart into the oven for 20 minutes and serve warm garnished with some flat leaf parsley.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home.