Finely chop the mushrooms in a food processor. In skillet combine first 7 ingredients and bring to a boil. Stir and simmer until reduced to a slightly moist paste (this takes time and needs to cool so start early).
Season tenderloin with pork roast rub or a savory seasoning of your choice. Place one pastry sheet on top of the other and roll it out until it measures approx. 18 x 15 inches. Spread 1/2 of cooled mushroom mixture over middle of puff pastry. Lay both pieces of pork on top, side by side, placing small end of one to big end of other, then spread remaining mixture over top of meat. Pull sides of pastry up and over tenderloin and seal with egg wash (1 egg mixed with 1 Tbl. water). Seal ends with egg wash, folding under, and then brush entire pastry with the egg wash. Flip tenderloin seam-side down and brush again with the egg wash. Make 4 or 5 small slits across top to vent.
Bake uncovered at 400° for 30-50 minutes, or until internal temp. reaches 135-140. Rest uncovered 20 minutes and then slice.
Serve with asparagus or broccoli and wild or wild & long grain rice.
This sounds like a lot of work, but the longest part is waiting for the mushrooms to reduce. The results are worth every minute.