To make the stuffing, put the porcini mushrooms in a heatproof bowl, cover with boiling water and soak for 20 minutes. Drain and chop, then set aside.
Heat the oil for the stuffing in a large frying pan over a medium heat. Add the onion and garlic and cook gently, stirring frequently, for 5-8 minutes, until golden. Add the cremini mushrooms and fry for 5 minutes, stirring occasionally, then stir in the chopped porcini mushrooms and the remaining stuffing ingredients. Season, then set aside to cool slightly. Wipe out the pan.
Lay the beef slices between sheets of plastic wrap and pound as thinly as possible using a rolling pin. Place, side by side, on a board. Divide the stuffing among them, then roll up each slice and secure with wooden toothpicks. Lightly brush the beef with some of the oil, then roll in the peppercorns.
Heat the remaining oil in the pan, add the beef olives and fry over a medium heat to brown all over. Remove using a slotted spoon and set aside.
Add the onion and celery to the pan and cook for 5 minutes until softened. Add the potatoes, carrots and tomatoes and stir for a couple of minutes, then return the beef olives to the pan. (If your pan is not big enough, transfer everything to a large flameproof casserole dish.)
Pour in the stock and sherry and add the bay leaf. Slowly bring to a boil, then reduce the heat to low, cover and simmer for 20-25 minutes until the meat and vegetables are tender.
Lift out the beef olives using a slotted spoon and keep warm. Boil the liquid in the pan over a high heat to reduce to the desired consistency. Season to taste. Put the beef olives back into the pan and serve sprinkled with parsley.
Cook's tip: To prepare this meal in advance, follow the recipe to the end of step 5, and chill the braise for up to a day in the refrigerator. Then continue from step 6, allowing 5 minutes extra cooking time.
Each serving: 35.5 g protein, 23 g fat of which 4.5 g saturates, 24.5 g carbohydrate, 8.5 g fibre, 484 Calories