Trim fillet, if needed of all the fat and sinews.Season with salt and pepper.Heat some oil in a large pan and quickly. You don't want to cook the beef, just sear so you seal in the juices. Remove and allow to cool.fry the seasoned beef all over until it's brown.Brush generously with the mustard.

Roughly chop the mushrooms and blend in a food processor to form a puree.Heat a skillet until hot. Add the puree of mushrooms and season with salt and pepper. I also added some onion powder. Cook without any oil/butter until it is dry and all the water has evaporated. The mixture should be sticking together in the form of a paste. Set aside and cool.

Roll out a generous length of cling film, lay out the four slices of Prosciutto ham, each one slightly overlapping the last. Spread the mushroom mixture evenly over the ham. Place the beef fillet in the middle.Roll the prosciutto and mushrooms over the beef into a tight log shape. Twist the ends to secure the clingfilm.Refrigerate for 10 -15 minutes, this allows the Wellington to set and helps keep the shape.

Roll out the pastry quite thinly to a size which will cover your beef. Unwrap the meat from the cling film. Egg wash the edge of the pastry and place the beef in the middle.Roll up the pastry, cut any excess pastry off the ends and fold neatly to the 'underside'. Turnover and egg wash over the top.Chill again to let the pastry cool, approximately 5 minutes. I let mine chill for about 20 minutes while I cleaned up. You will also want to preheat your oven to 425 F.

Egg wash again before baking. I placed my beef loaf unto a parchment lined baking sheet. This helps with the clean-up. Bake at 425 F for 10 minutes on middle rack. I then moved the sheet pan to the lower middle rack, for an additional 20-30 minutes. The total baking time should be about 35 - 40 minutes, depending on the size. Mine took about 40 minutes for the larger piece and 3o minutes for the smaller piece.Rest 8 -10 minutes before slicing. Serve with potatoes and salad. ~ If , you like your beef more well done, you can cook it longer. Just make sure you cover the puff pastry lightly with a foil so that it won't burn on you. Use an instant thermometer, if need be.

TIP:

1.When sauteing mushrooms, make sure they are completely dry. It should clump up on you and sort of form a paste. If you don't extract all the water from the mushrooms, you will have a soggy puff pastry.

2. I baked mine at 425 , 10 minutes on the middle rack and an additional 30 minutes on the lower rack so that the puff pastry would not burn on top.