Prepare tenderloins, trimming fat and the thin tail at the end (reserve tail end for another use).
Butterfly them for stuffing, making a 1-inch deep incision down the length of each - do not cut all the way through.
Stuff each tenderloin with half the Boursin.
Roll tenderloins in prosciutto.
To do this, lay half the prosciutto slices in a single layer, overlapping them slightly.
Place stuffed tenderloin at the base of the prosciutto and roll to cover.
Do the same thing with the second tenderloin.
Sear in 1 tbsp olive oil in a large skillet over medium-high heat until prosciutto is brown and crisp on all sides, 5-8 minutes.
Chill thoroughly.
Thaw two sheets puff pastry and roll each to a 16 x 12 inch rectangle.
Wrap pork and transfer to a parchment-lined baking sheet.
Combine egg and water and brush wrappers with mixture.
Then decorate with pastry vines and cutouts (leaves/stems).
Cover with plastic; chill 1 hour or up to 24 hours.
Preheat oven to 400 degrees with rack in lower third of the oven.
Brush with more egg wash for good browning; bake tenderloins 30-35 minutes or until golden, to about 170 degrees.
Let rest 5 minutes before slicing.
To serve, trim off the ends (they're doughy), and then slice into 1 1/2 inch thick pieces.