I have been making this recipe for a long time. I'm not sure where I got it, but the reaction of my family when they tasted this recipe told me it was a "keeper". They absolutely loved this pork tenderloin, and said it was their favorite dinner! It is mine too, so I hope you enjoy it.
Combine spinach, cheese, chorizo (or salami) and 1/4 teaspoon salt in a bowl.
In another bowl, combine garlic, 1 tablespoon oil and the remaining 1/4 teaspoon salt; set aside
To butterfly the tenderloin, lay it on a large cutting board. Holding the knife blade flat and parallel to the board, make a lengthwise cut through the center of the meat, stopping short of the opposite edge so the tenderloin remains in one piece. Open as you would a book.
Spread the spinach mixture in the center of the pork, leaving a 1-inch boarder all around. Starting at a long side, roll up pork to enclose the filling. Fold in the short sides as you roll, to keep filling from falling out. Tie kitchen string firmly lengthwise around the roast to secure the two ends, then tie it crosswise at 2-inch intervals.
Heat remaining 1 tablespoon oil in a large ovenproof skillet over medium-high heat. Reduce the heat to medium and brown pork on all sides, 4-6 minutes total. Brush top with reserved garlic mixture, season with pepper. Transfer pan to the oven and roast pork until an instant-read thermometer inserted into the thickest part of pork registers 145 degrees...15 to 20 minutes. Let rest on a clean cutting board for 5 minutes before slicing.