Season the 800g (1lb 12oz) pork fillets with salt and pepper. Heat 1 tablespoon oil in a frying pan and fry the pork fillets until browned on all sides, turning frequently. Set aside to cool.
Add 15g (½oz) butter to the pan and fry one chopped onion until softened. Then stir in 2 chopped cloves of garlic and cook for another minute.
While the onion is cooking blitz 200g (7oz) mushrooms in a food processor until very finely chopped. Add to the pan. Stir in 1 tablespoon brandy (or water if preferred) and cook the mushrooms for about 8-10 minutes until softened and any liquid has evaporated.
Season the mushrooms well with salt and pepper. Add 1 teaspoon dried sage, then mix in 150g (5oz) finely chopped chestnuts. Allow to cool.
Lay a large sheet of baking parchment on a work surface and place the 5 slices of Parma ham in the middle overlapping slightly to form a large rectangle.
Spread the chestnut and mushroom mixture over the ham. Place the pork fillet on top then use the parchment to roll the ham tightly around the pork.
Unroll the puff pastry and brush the surface with beaten egg. Carefully transfer the pork to the centre of the pastry. Wrap the pork in the pastry, Trimming away excess and using to patch up the pastry to completely enclose the pork if required.
Place seam side down on a greased baking sheet. Chill until ready to bake.
Preheat the oven to 200℃ (180℃ fan)/400°F/gas mark 6. Brush the surface of the pastry with beaten egg and sprinkle with Parmesan cheese. Bake for 30-40 minutes until the pastry is risen and golden borwn.
Nutrition information is calculated usingan online nutrition database - is approximate and is meant as a guideline only. (It does not include seasoning with salt and pepper.)