Preheat the oven to Gas Mark 7, 220°C, fan 200°C. Using a pastry cutter or saucer, cut out 4 x 12cm (5in) circles of pastry and place on a lined baking sheet. Bake for 10 minutes or until golden and crisp. Remove from the oven and leave them to cool.
Cut out 4 x 14cm (5½in) circles of pastry and set aside on nonstick baking paper. Use the trimmings to cut out 12 leaves as decoration for the Wellingtons. Place the leaves on the baking paper beside the circles and chill.
Remove the stalks from the Portobello mushrooms. Heat half the oil in a large frying pan and fry the whole mushrooms over a high heat for 3-4 minutes on each side until golden and cooked through. The mushrooms will release lots of juices, so leave them on the heat, turning occasionally, until the liquid is re-absorbed. Remove from the pan and drain on kitchen paper.
Soak the porcini mushrooms in boiling water for 10 minutes. Drain them, reserving the soaking water, then chop finely.
Place the frying pan back over a medium heat with the remaining oil, add the shallot, chestnut mushrooms and thyme leaves, season well and fry for 3-4 minutes.
Add the garlic and chopped porcini and fry for another 3-4 minutes or until all the liquid has been absorbed.
Put the spinach into a colander, pour boiling water over to wilt it, and squeeze out the excess water by pressing with a wooden spoon. Place on a chopping board, squeeze over some lemon juice and season well. Toss it all together and chop roughly.
Divide the chopped spinach between the cooked circles of pastry, making sure you leave a 1cm (½in) border of pastry clear. Now divide the chopped mushroom mixture and carefully spoon over the spinach. Add a slice of Camembert and top each circle with a Portobello mushroom. Season well.
Brush the border of each circle with beaten egg, then gently stretch the larger circle of pastry over the whole thing, trying not to push a hole in it or trap air under it. Press the pastry edges together with your fingers and chill the Wellingtons for 10 minutes.
Once chilled, press the edges firmly with a fork, and neaten with a sharp knife to make even circles. Then brush the Wellingtons all over with beaten egg, decorate each one with 3 pastry leaves (also brush over with egg) and chill until ready to bake.
Bake for 25 minutes in the preheated oven, or until golden brown and puffed up, then allow to cool for a few minutes. Serve with rocket salad dressed with lemon juice and extra-virgin olive oil.
These parcels can be prepared in advance until step 10, then chilled for up to 2 days.
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