Prepare and Sear the Beef: Pat the beef fillet dry with kitchen paper and season it generously all over with salt and pepper. Heat the olive oil in a heavy-based frying pan over a high heat until it's almost smoking. Carefully sear the fillet on all sides for about 30-60 seconds per side, until you have a deep brown crust. You are not cooking it through, just colouring the outside. Immediately remove from the pan and place on a plate to cool completely. Once cool, wrap it tightly in cling film and chill in the fridge for at least 30 minutes.

Make the Duxelles: While the beef chills, make the mushroom mixture. Place the mushrooms in a food processor and pulse until they are very finely chopped. Be careful not to turn them into a liquid paste. You can also do this by hand if you have the patience!

Cook the Duxelles: Melt the butter in the same frying pan over a medium heat. Add the finely chopped shallots and cook gently for 3-4 minutes until softened. Add the chopped mushrooms and thyme leaves. Cook, stirring occasionally, for 10-12 minutes. The mushrooms will release a lot of water. Keep cooking until all the liquid has evaporated and the mixture is a thick, dry paste. This step is crucial to avoid a soggy pastry base. If using, pour in the sherry or brandy and let it bubble away until evaporated.

Cool and Finish the Filling: Scrape the duxelles mixture into a bowl and season well with salt and pepper. Let it cool completely. Once cool, stir in the liver pâté until well combined.

Prepare the Pastry and Beef: Lightly flour your work surface and roll out the puff pastry into a rectangle roughly 3mm thick. Cut the pastry into 12 equal squares (approximately 10cm x 10cm). Unwrap the chilled beef fillet and cut it into 12 equal cubes.

Assemble the Wellingtons: Spread a thin layer of the mushroom and pâté mixture onto the centre of each pastry square. Place a cube of seared beef on top. What works best for me is to then brush the edges of the pastry with a little of the beaten egg.

Wrap and Chill: Bring the four corners of the pastry up to meet in the middle, over the beef. Pinch the seams together firmly to seal the parcel completely. Place the parcels seam-side down on a baking tray lined with baking paper. You can, at this point, chill them in the fridge for up to 24 hours. Chilling helps the pastry stay firm and puff up beautifully.

Bake to Perfection: When ready to bake, preheat your oven to 200°C (180°C fan). Brush the tops of the mini wellingtons all over with the remaining beaten egg. Using a sharp knife, gently score a pattern on top of each one if you like. Sprinkle with a little flaky sea salt. Bake for 15-20 minutes, or until the pastry is deeply golden brown, crisp, and puffed up.

Rest Before Serving: Let the Mini Beef Wellingtons rest on the tray for 5-10 minutes before serving. This allows the beef to relax and the juices to redistribute, ensuring a tender bite.