Instructions

1. Preheat oven to 400F (205C).
2. Make the duxelles by blending the mushrooms, onions, garlic salt, and olive oil together until pureed.
3. Then heat the mixture in a pan for 10 minutes on medium heat.
4. Place a large piece of cling-film onto the counter and place the pieces of prosciutto side-by-side (overlapping slightly) to form a rectangular layer.
5. Spread the duxelles over the prosciutto layer.
6. Sprinkle the 1/2 tablespoon of salt over the filet mignon and pan sear the filet mignon in 2 Tablespoons of olive oil.
7. Spread the 1 tablespoon of mustard on the seared filet mignon and place in the middle of the prosciutto and duxelles layer.
8. Use the cling-film to wrap the prosciutto around the filet mignon. Then wrap the cling-film around the package to secure it. Use a second piece of cling-film to pull the prosciutto-wrapped package tighter together. Place in fridge for 15 minutes.
9. Mix all the pastry ingredients together in a bowl (make sure to put in 1/2 the whisked egg and to leave the other 1/2 for the egg wash). Use your hands to knead the dough for a few minutes.
10. Roll the pastry out to approx. 1/3-1/4 inch thick on a piece of aluminum foil (the pastry will be a bit crumbly).
11. Remove the cling-film from the refrigerated prosciutto-wrapped beef and place prosciutto-wrapped beef in the center of the pastry.
12. Carefully pull up the 2 long ends of the pastry using the aluminum foil. Use your hands to push together the pastry on the other 2 ends and to fill up any cracks and gaps. Smooth the pastry out gently.
13. Wash the pastry with the egg wash (from the whisked egg).
14. Carefully cut 2 slits on the top of the pastry to allow air to escape.
15. Carefully transfer the Beef Wellington onto a greased baking tray and bake for 25-30 minutes (it should be pink when you cut into it).
16. To serve, carefully cut the Beef Wellington in half (the pastry will still be delicate, so it may crumble on the sides).