Remove the pork from the refrigerator about 1 hour before you intend to roast it. Season it all over with freshly ground black pepper. Leave to come to room temperature.

Meanwhile, begin preparing the duxelles. Melt the 50 g (2 oz) butter and saute the finely chopped onion for 3—4 minutes. Add the finely chopped mushrooms and the powdered thyme, then season to taste with salt and pepper. Cook the mixture for 30—40 minutes, or until there is no liquid

left. Add the parsley and breadcrumbs to the pan, mix in the beaten eggs and heat through to lightly set the eggs. Leave to cool.

Heat the 40 g (1 1/2 oz) butter in a frying-pan until it is foaming, and quickly sear the fillet on all sides. Leave it to cool.

Heat the oven to 200°C (400°F) gas 6. Roll out the puff pastry to 3 mm (1/8 in) thickness, and cut a rectangle, about 25 cm (10 in) wide, and 5 cm /2 in longer than the fillet. Reserve the pastry trimmings.

Spread half the duxelles down the centre of the pastry rectangle and place the fillet on top. Spread the remaining duxelles on the fillet and top with the Parma ham. Fold one side of the pastry over the fillet. Brush the upper surface with a little beaten egg, then fold over the second side to overlap the first, and press the edges together to seal. Roll the pastry ends out flat taking care not to stretch the pastry, brush the upper side of the roll with beaten egg, fold over the ends and press together to seal.

Place the pastry-wrapped fillet, joins downwards, on a lightly dampened baking sheet. Make 3 holes in the top to allow the steam to escape, and decorate around the holes with 'leaves' made from pastry trimmings, attaching them with a little beaten egg. Brush the pastry all over with beaten egg, and lightly score the top with a knife, crossways, diagonally or in V-shapes.

Bake for 40 minutes, until the pork is thoroughly cooked and the pastry is puffed up and golden brown. Slice and serve.