1 whole egg
1 tablespoon water
1-oz dried apple rings (don't buy them, you can make them here)
1 whole pork tenderloin, around 1lb but normally they are tough to find that small
3oz thinly sliced prosciutto ham
1/4 teaspoon kosher salt
1/4 teaspoon fresh thyme
All purpose flour
1 sheet of puff pastry, thawed completely
1 tablespoon whole-grain mustard
1. Place the rack in the bottom third of the oven and preheat to 400F
2. Whisk the egg and water in a small bowl and set aside. Using kitchen scissors cut the dried apple rings up to the size of a medium dice.
3. Trim the pork tenderloin of any excess fat and sliver skin (if you don't remove the sliver skin the tenderloin will curve while cooking). If needed slice the tenderloin down the middle lengthwise, creating 2 separate pieces. Lay the tenderloin pieces next to each other head to tail, so when laid back together they are the same size at the ends.
4. Lay out a 12x 16 piece of parchment on the counter and arrange the prosciutto in the center overlapping them enough to create a solid layer that is as long as the tenderloin. Place another piece of parchment on top and using a rolling pin, press the prosciutto together to help it adhere to one another. Remove the parchment and the sprinkle the prosciutto with the salt, pepper and thyme.
5. Set the tenderloin in the middle of the prosciutto. Spread the dried apples in between the two pieces of tenderloin and then then push them back together with the apples held between them.
6. Using the parchment paper to assist wrap the prosciutto around the tenderloin to completely enclose in a package.
7. Sprinkle the counter with flour, and roll out the pastry to approximately 12 x 14 inches. Spread the mustard thinly in the center of the pastry and lay the prosciutto wrapped tenderloin in the center of the pastry on top of the mustard.
8. Fold the puff pastry up and over the tenderloin, then roll completely to enclose, brushing the edges with the egg wash in order to seal. Turn the tenderloin over so the side of the tenderloin with the double thickness of pastry is underneath. Pinch the ends to seal.
9. Brush the entire pastry with egg wash. Place the tenderloin on a parchment lined sheet pan and bake for 25-30 minutes or until the pork reaches an internal temperature of 140F (I suggest using an oven thermometer to keep track - esp, if you have a really cool one like mine.)
10. Remove the tenderloin from the oven, transfer to a cooling rack and let rest for 10 minutes before slicing and serving. (While it rests the internal temperature will continue to rise another 20F and the juices will get partially absorbed. Don't omit this resting time or you will get undercooked pork!)