800g beef fillet (centre-cut)
¼ cup olive oil
450g mixed mushrooms, roughly chopped
2 cloves garlic, finely chopped
4 French shallots, finely chopped
1 tbsp thyme leaves
1 tbsp parsley, finely chopped
1 tbsp Dijon mustard
12 thin slices prosciutto
375gm good quality butter puff pastry
1 egg, lightly beaten
3 brown onions, thinly sliced
1 tbsp plain flour
400ml good quality beef or chicken stock
100ml red wine
1 tbsp Dijon mustard
1 ½ tsp Worcestershire sauce
2 tsp thyme leaves
Season beef and heat half the oil and 20gm butter in a large non-stick frying pan over high heat. Cook beef for 5 minutes or until browned on all sides. Set aside on a plate to cool.
Process the mushrooms in a food processor until finely chopped. Heat the remaining oil and butter in the same pan over high heat. Add the garlic and shallots and cook for 1 minute, then add the mushrooms. Cook for 12 to 15 minutes or until liquid has evaporated. Remove from the heat, season and stir through thyme, parsley and mustard. Set aside to cool for 20 minutes.
Lay a large sheet of cling wrap on a large chopping board, and arrange prosciutto lengthways, with slices overlapping. Evenly spread the mushrooms over the prosciutto. Place the beef on top of the mushrooms and wrap the prosciutto around the beef. Enclose tightly in the cling wrap and chill in the fridge for 45 minutes to 1 hour to firm.
Preheat the oven to 220°C (200° fan-forced).
On a lightly floured surface, roll the pastry out to a rectangle large enough to enclose the beef (around
3mm thick). Remove the beef from the plastic and place in the centre of the pastry. Fold one long side of the pastry over the beef and brush the edge with egg. Fold the other long side of the pastry to enclose the beef, press to seal, trim any excess pastry from underneath and turn the beef over. Trim excess from the ends of the pastry and tuck under the beef, gently pressing to seal. Place the beef parcel on a tray lined with baking paper and brush the parcel with egg. Decorate the parcel as desired with shapes from the pastry cut-offs (leaf shapes are traditional), brushing with egg. Decorate the remaining pastry using a fork to make decorative lines. Refrigerate the parcel for 10 minutes.
Cook the beef in the oven for 10 to 15 minutes, or until the pastry is golden. Reduce the temperature to 140°C (120° fan-forced), opening oven door for 1 minute to reduce heat quickly. Cook beef for another 25 minutes, then rest the beef for 8-10 minutes.
Meanwhile, to make the onion gravy, melt the butter in a non-stick frying pan over medium heat, add the onions and cook for 8 to 10 minutes or until softened. Reduce the heat to low, cover, and cook for 15 to 20 minutes, or until onions are browned. Add the flour and stir for 1 minute. Add the wine and reduce by half then add the stock, mustard and Worcestershire. Bring to the boil and then reduce to a simmer for 10 to 15 minutes, or until thickened. Season.
Cut the pastry ends from the beef parcel (if desired), cut beef in half, and then cut each piece in half again. Serve with onion gravy.