Season cut filet steak pieces with salt and black pepper on all sides.
Heat up a pan with the butter and olive oil and wait for it to get super hot.
Place meat into the pan and sear on both sides on high heat. Each side for about 2-3 minutes.
Take the meat from the pan and keep aside. Reduce heat in pan and continue to use to make the duxelles.
For the Mushroom Duxelle
Add olive oil to the same pan and keep on a steady heat.
Place cut shallot pieces into the pan and saute till they are cooked through.
Add cut mushroom and parsley together to the pan and stir cook occasionally so that they turn into a duxelles (that's how it's called).
When cooked halfway through you can choose to season with salt and pour wine over the duxelles over the mushrooms. Cook further until liquids are dissolved and you are left with cooked through mushrooms. Keep aside
To arrange Wellington
Prepare puff pastry by rolling it out. Cut one sheet into two, we will be using 2 sheets for 4 servings. *see Notes
Place cooked meat on a working board and cover with mustard paste. 1 Tablespoon mustard paste per meat steak.
Spread some of the mushroom duxelles over the steak with mustard.
Take a cut puff pastry sheet and cover the naked wellington steak with it. Carefully wrap the puff pastry around the steak and cut off excess dough. Close the dough at the bottom of the steak. Repeat the process with all wellingtons
Preheat oven to 400° Fahrenheit/ 200° Celsius.
Place beef wellingtons on a baking sheet or onto a baking dish.
Decorating the wellington with excess cut out shapes of puff pastry is optional.
Brush wellington parcels with egg yolk.
Bake at 400° Fahrenheit/ 200° Celsius for about 10-12 minutes or until golden brown on top. You can check if the meat is pink and cooked inside with the help of a meat thermometer.
Serve hot with a side dish and sauce of your choice. (see post for serving suggestions on top)
I forgot to show how I add the salt and wine in the video. Adding the white wine is optional anyway. I add salt and whine after the sauteeing the mushrooms half way through and reduce the mushrooms duxelles (that's how it's called) until no liquids are left while stirring continuesly.
I use store bought puff pastry rolls to save time. One roll can be used to wrap in two beef wellington with pastry. There will be leftover puff pastry, which you can use to decorate your wellingtons or you can use it for something else. I found this to be the easiest method. You can also choose to use one puff pastry sheet for 4 wellington too by cutting it into two, wrapping two wellington with pastry, taking the remaining pastry, rolling it out into two squares to wrap around the remaining two wellingtons. But keep in mind that you might get short on pastry.