Step 1
Sift the flour and salt into a large mixing bowl. Use your fingertips to rub the Trex into the flour until the mixture looks like fine crumbs. Add 4-5 tbsp chilled water and mix it in with a knife until the pastry clings together. Form the dough into a ball, then wrap and chill for 10 minutes.

Step 2
Preheat the oven to 200°C/fan oven 180°C/Gas Mark 6.

Step 3
Roll out the pastry on a lightly floured surface and use it to line a 20x30cm (8x12in) oblong tart tin. Line with a piece of foil or greaseproof paper and baking beans and bake ‘blind’ (i.e. without a filling) for 15 minutes. Meanwhile, boil the new potatoes in lightly salted water for 15 minutes.

Step 4
Take the flan from the oven and remove the foil or paper and baking beans. Reduce the oven temperature to 180°C/fan oven 160°C/Gas Mark 4.

Step 5
Drain and cool the potatoes, then slice them and place over the base of the flan. Cook the asparagus in boiling water for 2 minutes, rinse with cold water, then arrange over the top of the potatoes.

Step 6
Beat together the eggs, crème fraiche and Parmesan cheese. Season. Pour into the flan case, then bake for 30-35 minutes, until set. Best served warm.