Place the tenderloin on a cutting board and liberally sprinkle salt all over it (see NOTES regarding salt). Next, sprinkle the rub all over the tenderloin, using your fingers to help press it into the surface of the meat. Place in a dish and cover with plastic wrap. Refrigerate for 1 to 2 hours, or up to overnight.

In a medium saucepan over medium heat, bring the pure cranberry juice to a strong simmer. Simmer until reduced by about a quarter (usually about 10 minutes). Add the molasses and Sherry vinegar and simmer for another 5 to 10 minutes, until it is thick enough to coat the back of a spoon and has reduced another quarter cup (half cup reduction in total). Pour about half of the "mop" into a vessel to save for serving tableside. You'll use the rest for "mopping" the tenderloin as it cooks.

Heat your grill to medium heat. Add the marinated meat directly over the heat. Brush on the "mop" and grill for about 8 minutes, or until grill marks appear on the underside. Turn the tenderloin over, brush with the mop, and cook another 8 to 10 minutes, or until an internal temperature of 135 to 140°F is reached. Brush on the mop several times during the grilling process.

Remove the meat from the grill and place on a cutting board. Use some of the reserved mop to brush another layer of the mop over the top of the tenderloin. Allow the tenderloin to rest for about 10 minutes.

Cut the meat into ½-inch slices and serve immediately, passing the extra cranberry reduction mop at the table.