Step 1
Sift the flour and salt into a large mixing bowl and rub in the Trex with your fingertips until the mixture looks like fine crumbs. Add 3-4 tbsp chilled water and mix it in with a round-bladed knife until the pastry clings together. Use your hand to form the dough into a ball. 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 23cm (9in) flan ring or flan dish. Line with a piece of crumpled foil or greaseproof paper and baking beans and bake ‘blind’ (i.e. without a filling) 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
To make the filling, heat the Trex in a frying pan and fry the spring onions for 3-4 minutes until soft. Cool, then scatter over the base of the flan with the asparagus and smoked salmon.

Step 6
Beat together the eggs and soft cheese until smooth, then mix in the milk and herbs. Season. Pour into the flan case, then bake for 30-35 minutes, until set.