Recipe for Pork-Wellington - First dry and season the pork tenderloin, keeping it simple with salt, pepper, and olive oil. Sear the tenderloin on the grill or on the stove for simplicity. This takes 3 minutes for each side.
Once this is done you can further season the beef with herbs like thyme, English mustard, anything you want. Next prepare the mushrooms. Puree or finely chop ~3 cups worth of mushrooms. Next, cook the puree to get the water out, this takes about 8-10 minutes on medium-low heat. The mushrooms give flavor and also help keep the puff pastry from getting soggy.
Now assemble the Wellington. Take a defrosted puff pastry and roll it out somewhat. You want it big enough to surround the tenderloin and not too thin. Line the puff pastry with prosciutto ham, or another type ham of your choice. Then spread the cooked mushroom puree on the ham. Place the tenderloin in the middle then egg wash the edges and wrap. Egg wash the outside and chill in the refrigerator for twenty minutes.
Lastly, place the Wellington in a 400° oven for 25 to 30 minutes.
Here is a video to show you all these steps.