To begin, make the pie crust. Mix the salt and flour together and then sift into a bowl. Add the fats and cut them into the flour to break them down a little, then use your fingertips to crumb the flour and fats together, making sure your hands aren’t too warm. Get as much air incorporated as possible and work gently so you end up with a nice light crumb.
Add a little cold water and combine with the crumb until you have a perfect pastry. Cling film the pastry and leave to rest in the fridge.
Prepare one of the swedes for the mash by pricking it all over with a fork. Place on a bed of rock salt on a tray and cook in the oven for approx. 45 minutes, turning frequently.
To prepare the baby turnips, add them to a pan and cover with cold water. Add the vinegar, salt, sugar and thyme.
Bring to the boil, then reduce the heat to a gentle simmer for 5–6 minutes. Remove the turnips and allow to cool. Pass the cooking liquid through a sieve and save for reheating later.
Meanwhile, prepare the beef. Trim the chateaubriand, keeping the trimmings quite chunky for the pie. Let the meat come to room temperature before cooking.
When the pastry has rested, remove from the fridge and roll thinly. Return the pastry sheet to the fridge once more.
Now prepare the pie filling. Heat some butter and a little oil in a sauté pan and add the finely chopped carrot, potato and celery. Cook slowly until the vegetables are quite tender.
Take all of the vegetables out of the pan and re-heat the pan ready for the beef.
Season and dust the beef trimmings lightly in flour. Heat some oil in the sauté pan and add the beef, sealing nicely until well coloured. Don’t cook for too long – this is fillet, after all!
Return the vegetables to the pan and add a splash of reduced beef stock to coat the beef nicely and deglaze the pan. Stir in the beef fat and chopped parsley. Set aside.
Once the baked swede is cooked, cut in half and scoop out the flesh with a spoon. Place in a pan and crush with a fork or potato masher, add a few knobs of butter, salt and pepper to taste.
Cut the raw swede into 5mm slices, cut into discs with a 3cm cutter and cook in a small pan of gently simmering water with a pinch of salt and a knob of butter until tender. Season with a twist of black pepper.
To form the pies, use a cutter the same size or slightly larger than your 4 pie dishes to cut out rounds of the pastry, then cut small holes in the centre.
Use some egg yolk to brush the edges of the pie dishes, then fill with the beef trimmings. Top with an oyster, then place the pastry lids on top. Brush with egg yolk, brushing in one direction for neatness, then season the lid with fleur de sel and freshly ground black pepper. Cook in the oven for 8–10 minutes.
To cook the chateaubriand, add the beef fat to a hot pan. Once sizzling, add the beef, reduce the heat slightly and cook, turning occasionally, until deeply browned all over.
After about 8 minutes, add the butter and allow to foam. Spoon the foaming butter over the meat, continuing to cook and refreshing the butter as necessary. The whole cooking process should take around 15 minutes.
Rest the beef for at least 10 minutes in a warm place before carving to allow the juices to be reabsorbed by the meat.
Reheat the turnip cooking liquid in a pan and add a knob of butter. Whisk to emulsify, then add the turnips and turnip tops, cooking for long enough to just heat through.
Carve and plate the chateaubriand slices with quenelles of the swede mash, swede discs, turnips and turnip tops. Serve the pie on the side.