Trim any silver skin off the pork tenderloin. Pat the pork completely dry with paper towels and season generously on all sides with kosher salt and coarse black pepper.

Heat oil in a large skillet over medium-high heat until shimmering. Place the pork in the hot pan and sear for 3-4 minutes per side, until a deep golden-brown crust forms. Transfer the pork to a plate.

Reduce heat to medium. Add the minced shallot to the skillet and cook for 2 minutes until soft. Add garlic and cook for 30 seconds more until fragrant. Pour in the white wine to deglaze, scraping all the browned bits from the bottom of the pan. Allow it to bubble and reduce by half.

Whisk in the Dijon and whole grain mustards, then slowly whisk in the heavy cream. Bring to a simmer and cook for 3-4 minutes, until the sauce has thickened enough to coat a spoon. Season with salt and pepper to taste.

Return the pork tenderloin and any juices to the skillet. Spoon sauce over the top. Reduce heat to low, cover, and cook for 5-10 minutes, or until an instant-read thermometer reaches 145°F (63°C). Transfer pork to a cutting board and let it rest for 5-7 minutes. Stir fresh parsley into the sauce. Slice the pork into thick medallions, arrange on a plate, and pour the sauce over top. Garnish with more parsley and black pepper.