Lightly oil an 18 cm (7 inch) flan tin and set aside.

Place the flour in a bowl and rub in the margarine until the mixture resembles fine breadcrumbs.

Gradually add about 15 ml (1 tbsp) chilled water to make a soft dough, then knead lightly for a few seconds.

Roll out the dough on a lightly floured surface and use to line the prepared tin. Flute the edges. Place a sheet of greaseproof paper and baking beans over the pastry and bake blind at 200°C (400°F) mark 6 for 15 minutes. Remove the beans and greaseproof paper from the pastry shell and bake for a further 5 minutes. Place on a rack to cool.

Meanwhile, place the potatoes and asparagus in a small, deep saucepan of boiling water so that the asparagus tips are above the water. Cover tightly and return to the boil. Reduce the heat and cook for 15 minutes.

Melt the margarine in a small frying pan, add the eggs and scramble until they are just setting. Remove from the heat and stir in the cheese and seasoning to taste.

Drain the vegetables. Chop the potatoes and the ends of the asparagus stalks, reserving the tips, and add to the eggs.

Fill the baked tart shell with the egg mixture, and top with the asparagus tips, halved lengthways and cut to fit the tart top as necessary. Serve the tart warm or cool.