Preheat your oven to 375°F/190⁰C.
Chop first four ingredients with the Food Chopper.
Remove any silverskin from tenderloins, pat dry. Using your hand, rub the garlic mixture over pork tenderloin, then season with salt to taste.
Heat oil in skillet over high heat until shimmering, then add in tenderloins, searing on all sides to brown. Place skillet in oven and bake approximately 15-20 minutes, or until pork reaches an internal temperature of 140⁰F/60⁰C.
Remove pork from skillet, and tent with foil on cutting board.
Add one tablespoon of oil to skillet over medium heat, and add in shallots; sauté just until tender, about 2-3 minutes. Add in port wine, rosemary sprig and peppercorns, and bring to a boil, scraping the bottom to release any browned bits. Reduce heat to low, and simmer until liquid is reduced by half. Remove from heat, and in butter and whisk to incorporate.
Strain the sauce if necessary (I did not find it to be) and serve on the side with the sliced tenderloin.