Bring the meat to room temperature.
Boil the kettle and pour 150ml boiling water into the measuring jug.
Add the porcini mushrooms and soak for 20 minutes.
Sift the flour for the pancakes into a bowl. Make a well in the centre and add the beaten egg and a little milk. Whisk until smooth. Add the remaining milk and continue whisking to a smooth batter. Cover and set aside to rest for 15 minutes.
Heat a little oil in the frying pan and when it’s hot, pour a ladleful of pancake batter and heat until the top is no longer liquid. Flip over and continue cooking until browned. Transfer to a plate lined with kitchen paper. Make the other pancakes and place on the plate with the other one. You should have four medium sized pancakes. Set aside.
Wipe the frying pan with kitchen paper and add the beef dripping.
Set over a high heat and, once the fat is sizzling hot, sear the beef fillet briefly on all sides until well browned and crusted. Season and leave to cool in the pan.
To make the pastry sift the flour and salt into a large bowl.
Cut the butter into very small chunks and add them to the bowl and stir them in loosely until all the butter chunks are coated in flour.
Add the cold water and bring together to a wet dough with a lumpy consistency.
Cover with clingfilm and place in the fridge for 30 minutes.
Place the chilled dough on a floured work surface and shape into a rectangular block.
Roll the dough to a rectangle three times longer than it is short, keeping the edges straight and even. The rolled-out pastry should have a marbled effect from the lumps of butter.
Fold the top third down to the centre, then the bottom third up and over that.
Give it a quarter turn and roll out again to the original sized rectangle.
Repeat the folding, turning and rolling out 3 more times or until the marbling effect has disappeared. Fold once more and place in the fridge for 30 minutes.
Remove the chilled pastry from the fridge and allow to come to room temperature.
Remove the porcini mushrooms with a slotted spoon and place in the small bowl. Reserve the liquid in the measuring jug.
Melt the butter in the saucepan and add the shallots. Cook over a medium heat until golden.
Add the thyme leaves and the mushrooms (including the chopped porcini mushrooms) and continue to cook until the mushrooms have softened.
Add 100ml of the Madeira and 50ml of the reserved porcini liquid. Turn up the heat and cook until most of the liquid has evaporated.
Stir in the cream and season to taste. Spread on a plate and place in the fridge.
Grease the baking sheet with a little oil or beef dripping.
On a lightly floured surface, roll out the pastry into a 25cm x 30cm rectangle that’s about 3mm thick, with one of the longer edges facing you.
Place the pancakes to fit the rolled-out pastry (trimming them into appropriate-sized oblongs). This helps to prevent any juices seeping into the pastry, making it soggy. Trim the pancakes to leave a 2cm border of pastry.
Spread the mushroom and cream mixture over the pancakes, leaving the 2cm border. Brush the borders with beaten egg.
Lift the cooled beef up with tongs and allow any blood to drip back into the frying pan. Lay it across the bottom of the pastry.
Reserve the unwashed frying pan for later.
Carefully roll up the pastry, ending with the seam side facing down.
Trim the edges of the pastry and tuck them in securely at each end to seal the parcel, using more egg wash as glue.
Use the back of a knife to make a crisscross design on the pastry making sure you don't cut right through it.
Transfer the Wellington to the baking sheet and place in the fridge for at least an hour but up to 24 hours. If you chill the Wellington for more than 2 hours you will need to slightly increase the cooking times.
Preheat the oven to 220C/425F/gas 7 at least 30 minutes before you are ready to bake the Wellington.
Remove the Wellington from the fridge and brush the pastry all over with more egg wash and sprinkle with poppy seeds.
Place the Wellington in the oven and bake for 25 minutes for medium rare, or 35 minutes for medium. You will need a meat thermometer to check when it’s done: medium rare 55-60C and medium 60-65C.
Remove from the oven and rest the Wellington for 10-15 minutes while you make the madeira sauce.
Place the pan you cooked the beef in back on the heat. There should be some remaining fat but if not add a little beef dripping.
Add the tablespoon of flour and stir into the fat and juices.
Add the remaining Madeira and scrape the pan to dislodge any crusty bits, then add the rest of the porcini soaking liquid, stir in with a hand whisk and cook until reduced a little and thickened slightly.
Season to taste and strain into a serving jug or gravy boat.
Transfer the Wellington to a serving dish and serve with the Madeira sauce.
