Preheat oven to 210°C.
Melt butter in a pan until foaming and sauté the onion and garlic until soft.
Add the mushrooms and Italian Herb and cook until the mushrooms are soft and all the liquid from the mushrooms has simmered off.
Add the KNORR Vegetable Stock Pot and stir until it has dissolved.
Remove the pan from the heat and allow the mushrooms to completely cool.
Transfer to a bowl and using a stick blender, blend to a chunky paste.
In the mean time heat cooking oil in a separate pan and brown the beef fillet on all sides for about 3-4 minutes per side, so that the fillet is well browned.
Remove the fillet from the pan and allow to cool then rub the mustard onto the fillet.
Lightly roll out the pastry until it is large enough for the fillet to fit comfortably in the middle of the pastry.
Spread the mushroom mixture over the pastry, leaving a border around the edges.
Place the whole beef fillet in the centre of the mushroom mixture and roll the pastry over and around the fillet so that it is completely sealed.
Trim off any excess pastry from the sides and pinch closed.
Using a pastry brush, brush the pastry with the egg wash and using a small knife cut diamond shaped slits into the top of the pastry.
Place onto a greased oven tray and into a preheated oven for 25-30 minutes or until the pastry is golden brown and flaky. Should you prefer your meat well done leave in the oven for a further 10 minutes, you may need to reduce the heat so that the pastry does not burn.
Using a lifter transfer the beef wellington to a serving platter and serve with KNORR Roast Meat Gravy.