1 pork tenderloin
2 tablespoons vegetable oil, plus more as needed
1 teaspoons salt, plus more as needed
1 tablespoon Dijon mustard
1 tablespoon stone ground mustard
1/4 teaspoon ground black pepper
2 Red Delicious apples, cored and sliced
1 large red onion, sliced
1.5 cups apple cider or natural apple juice (dark brown opaque, not honey colored)
1 tablespoon butter
1 tablespoon flour

1 pork tenderloin 2 tablespoons vegetable oil, plus more as needed 1 teaspoons salt, plus more as needed 1 tablespoon Dijon mustard 1 tablespoon stone ground mustard 1/4 teaspoon ground black pepper 2 Red Delicious apples, cored and sliced 1 large red onion, sliced 1 5 cups apple cider or natural apple juice (dark brown opaque, not honey colored) 1 tablespoon butter 1 tablespoon flour

Heat oven to 425 degrees F (220 degrees C).

Trim the tenderloin of any silver skin. Pat pork dry with paper towels.
Then, using your hands, rub the tenderloin all over with vegetable oil, sprinkle with 1 teaspoons of salt, and rub until tenderloin is evenly coated.

Heat a tablespoon of oil in a large cast iron skillet or heavy-bottomed oven-safe frying pan over medium heat. Add the pork tenderloin and cook, turning occasionally, until evenly browned all over. This should take about 12 minutes. Transfer the browned pork to a large plate or cutting board.

Check the pan, if it looks dry add 2 to 3 teaspoons of additional oil. Add the onions and cook until browned and soft, about 5 minutes. Next add the apples and cook, stirring occasionally, until lightly browned around edges, about 2 minutes.

While the apples and onions cook, rub the pork all over with both dijon and stone ground mustard, slather it on generously. Sprinkle it with some black pepper.

Place the pork tenderloin on top of the apples and onions and slide into the oven. Roast 15 minutes or more, depending on thickness of your tenderloin, until an internal thermometer inserted into the thickest part registers between 145 and 150 degrees F (63 and 65 degrees C).

Transfer pork to a large plate and cover with aluminum foil. Let rest about 10 minutes.

While the pork rests, place the pan with apples and onions back onto the stove and turn heat to medium. Add apple cider and use a wooden spoon to scrape the pan, lifting any brown bits from the bottom. Bring to a simmer and cook until reduced. Add butter and stir until melted. Sprinkle flour across the sauce, let it sit for a few seconds, and then stir it in to thicken the sauce.

Slice pork into 1-inch slices then serve on a bed of the apples and onions with pan sauce drizzled on top.