Instructions: Preheat the oven to gas mark 7 (220C,425F). Finely chop the onion and mushrooms and crush the garlic.

Fry the onion in the margarine in a large saucepan for 10 minutes. Add the mushrooms and fry for 20-30 minutes, until all the liquid has evaporated.

Remove from the heat and add the garlic, parsley, breadcrumbs, lemon juice, salt and pepper to taste. Allow the mixture to cool.

Roll 1/3 of the pastry into a 6 x 12 inch (15 x 30 cm) rectangle. Place on a baking sheet, spoon the mushroom mixture on top (heaping it up in the centre) and brush the edges with water.

Roll the remaining pastry into a 9 x 12 inch (23 x 30 cm) rectangle. Fold the pastry in half lengthways and make diagonal cuts to within an inch or so of the edges for a decorative finish. Ease the pastry on top of the mushroom mixture and open out to cover.

Press the edges together and trim away any excess pastry. Brush with the egg yolk or margarine, and bake for 30 minutes until golden-brown. Serve hot or warm.

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