500 g (1 lb) mushrooms, halved (or quartered, if very large)
200 g (7 oz) cream cheese
1 teaspoon dried tarragon or 1 tablespoon chopped tarragon
500 g (1 lb) puff pastry
flour, for dusting
1 small egg, lightly beaten
salt and pepper
Melt the butter in a large frying pan and cook the leeks over a medium heat for 3 minutes, stirring occasionally, until they begin to soften. Add the mushrooms and continue to cook for a further 4–5 minutes until tender and lightly golden, then stir in the cream cheese and tarragon.
Meanwhile, roll out the pastry on a lightly floured surface and cut into 4 x 20 cm (8 inch) circles. Brush a 1 cm (1/2 inch) border with a little beaten egg.
Season the leek and mushrooms with a pinch each of salt and pepper and divide the mixture between the 4 circles. Now bring up 2 sides of the pastry to encase the filling, crimping the pastry together with your fingers to seal the edges.
Arrange the filled pastries on a baking sheet, brush with the remaining beaten egg and cook in a preheated oven, 200˚C (400˚F), Gas Mark 6, for about 18 minutes until puffed up and golden. Serve warm.