Preheat the oven to 190°C, Gas Mark 5.
To make the mushroom duxelle mix, put them in a food processor or a blender and pulse to a rough dice. Heat the butter in a frying pan and fry the onion and garlic until softened but not coloured. Add the chopped mushrooms and cook, again without colouring, for 5 minutes. Season, then add the thyme and sage. Leave to cool.
For the pancakes, mix the flour, eggs and milk in a jug. Heat the butter in a small frying pan and pour two-thirds of it into a small bowl to keep aside for brushing the pan between pancakes.
Pour a small amount of the batter into the frying pan and swirl it around to cover the base of the pan. Cook for 1-2 minutes and then flip and cook for another minute.
Remover the pancake from the pan to a plate and continue to cook 5 more pancakes. Layer the pancakes with greaseproof paper in between and leave to cool.
Season and seal the beef fillet and set aside.
Mix the cooled mushroom duxelle with the pate in a mixing bowl. Brush the large sheet of pastry with the egg wash. Layer the pancakes over the top of the pastry so that it is covered and then use a palate knife to spread the mushroom mixture on top.
Place the beef on top of the mushroom mixture and roll up the pastry, making sure that the beef is completely surrounded by the mushroom mix and the pancakes and well sealed. Leave to chill.
Next take the extra puff pastry and cut out holly leaf shapes, using the egg wash to stick them to the beef Wellington.
Place the Wellington on a baking tray and brush the top with the beaten egg. Bake in the oven for 30 minutes, or until your liking.
Recipe courtesy of Matt Tebbutt