Preheat oven to 400*. Have at the ready a roasting pan with a rack.
Butterfly tenderloin by slicing lengthwise almost all the way through, to about 1/4 inch. Cover with plastic wrap and pound with meat mallet to about 1/6 to 1/8 inch thickness. Remove plastic wrap.
Season both sides of the tenderloin with salt and pepper.
Layer pancetta, then provolone, then spinach onto the tenderloin. Roll tightly, secure with cotton twine.
Place rolled tenderloin into the roasting pan. Cover and bake at 400* for 10 minutes, then reduce oven temperature to 350*. Continue to bake for 1 hour, or until internal temperature reaches 160*.
Once temperature reaches 160*, remove from oven and rest 5-10 minutes.
While the meat is resting, make a pan sauce from the drippings. Serve slices of the roulade with the sauce.
**I frequently change the stuffing ingredients. I have used sun dried tomatoes, feta, and spinach; gruyere, ham, and asparagus; bacon, mushroom, and mozzarella; sausage and spinach. Use your imagination!