Preheat your oven to 400°F (200°C).
Pat the pork tenderloin dry with paper towels and season all sides generously with salt and pepper.
In an oven-safe skillet, heat the olive oil over medium-high heat.
Once hot, add the pork tenderloin and sear it for about 3-4 minutes on each side, until golden brown all over.
Add the butter, minced garlic, thyme, and rosemary (if using) to the skillet. Baste the pork with the melted butter for extra flavor.
Transfer the skillet to the preheated oven and roast for about 15-20 minutes, or until the internal temperature reaches 145°F (63°C).
Remove the pork from the oven and let it rest for about 5-10 minutes before slicing.
While the pork is resting, use the same skillet over medium heat (you can add a splash of white wine or broth to deglaze the pan if desired).
Stir in the heavy cream, Dijon mustard, and whole grain mustard.
Bring the sauce to a simmer, whisking to combine, and cook for about 3-5 minutes until the sauce thickens slightly.
Season with salt and pepper to taste.
Slice the pork tenderloin into medallions and arrange them on a serving plate.
Drizzle the creamy mustard sauce over the pork and garnish with fresh chopped parsley.
