Whiz the flour, butter and a pinch of salt in a food processor until the ingredients resemble very fine breadcrumbs. Add one beaten egg and 2 tablespoons of cold water and pulse until the mixture just begins to come together.Turn out on to a floured work surface and knead very lightly. Cut a chunk from the pastry - about one-third of the total. Wrap both pieces and chill for at least 30 minutes.

Preheat the oven to 200°C/180°C fan oven/Gas Mark 6. Roll out the larger piece of pastry on the floured work surface to form a 28cm (11 in) diameter circle, then use it to line a 20 cm (8 in), 5 cm (2 in) deep, loose-bottomed tin.Tidy the edges and prick the pastry base with a fork.

Line the pastry with greaseproof paper and baking beans, banking the beans up against the sides. Place the pastry tin on a baking sheet and bake for 25 minutes. Remove the paper and beans, brush the inside of the pastry with a little of the other beaten egg. Return to the oven for 5 to 10 minutes, or until the pastry is almost cooked, then cool. To make the filling, mix the eggs and yolks with the creme fraiche and dill, then season. Heat the butter in a frying pan, and fry the mushrooms over a high heat for 1 to 2 minutes. Season with salt and black pepper and set aside to cool.

Put the asparagus in a pan of boiling water, return to the boil, then drain. Plunge into iced water for a few minutes, then drain. Arrange half the salmon in a cartwheel pattern in the bottom of the pastry. Scatter the mushrooms over, arrange the asparagus in the same pattern on top, then finish with the remaining salmon. Pour over the creme fraiche mixture to within 1 cm (1/2 in) of the top of the pastry case. Brush the inside rim of the pastry with some of the remaining beaten egg. Roll out the remaining pastry, cut into a 25 cm (10 in) circle and position on top of the filling.

Seal the raw pastry gently to the inside rim of the cooked pastry. Brush with the remaining beaten egg, make a steam hole in the middle of the pie and decorate with a knife. Put the baking tray in the oven, set at 200°C/180°C fan oven/Gas Mark 6, to preheat. Bake the pie on the tray for 40 minutes until golden and the filling is cooked - cover with foil if it becomes too brown.To check the pie is cooked, insert a skewer in the centre for 30 seconds - it should feel hot. Place the pie on a cooling rack, in the tin, for 1 hour to serve warm or 3 hours, then remove from tin and slice up for a picnic.