Preheat oven to 425 degrees with the rack in the middle. In a small bowl, combine the dijon mustard, honey and rosemary. Stir to combine, set aside.

Preheat an oven safe skillet over high heat. While it is heating up, pat pork loin dry with a paper towel and season generously with salt and pepper on all sides. When the skillet is hot, sear the pork loin on all sides until golden brown, about 3 minutes per side. Top with the rosemary honey mustard mixture and spread evenly to coat the pork loin, but reserve 1 tablespoon of the mixture for the pan sauce.

Transfer the pork loin in the oven safe skillet to the oven to finish cooking. Cook until the meat is 145 degrees, about 15 minutes. Remove from the oven and allow to rest for a few minutes.

While the meat is resting, make the pan sauce in a skillet over high heat. Combine the wine, apple cider vinegar, 1 tablespoon of the rosemary honey mustard mixture. Stir to combine and cook until it has reduced by half. Give it a taste, and add more honey to the sauce if desired.

Slice the pork loin into 1/2" thick slices, and top with the pan sauce.