Cook pork tenderloin to 145 degrees in an oven-proof skillet or sautee pan. (I'm bad with big pieces of meat. I have no idea how long that takes.) When the tenderloin is done, remove from pan, and let rest for 15 minutes before slicing.
While pork is resting, make the sauce.
1 cup white wine
1/3 cup loosely packed, roughly chopped flat-leaf parsley, or 1-2 tablespoons dried parsley
coarse-grained salt (Kosher or sea salt) and cracked black pepper
Over high heat, add the wine to the pork drippings, scraping the bottom of the pan. Reduce wine to 1/3 cup. Add parsley, and salt and pepper to taste. It doesn't make a lot of sauce like a gravy, but just enough to drizzle over the sliced tenderloin.