Prepare the Marinade:

In a mixing bowl, combine olive oil, soy sauce, red wine vinegar, lemon juice, Worcestershire sauce, garlic, parsley, dry mustard, and freshly cracked black pepper. Stir until well blended. Reserve 3 tablespoons of the marinade in a separate container for the sauce.

Marinate the Pork:

Place the pork tenderloin in a resealable plastic bag and pour in the remaining marinade. Seal the bag, ensuring the meat is fully coated, and refrigerate for a minimum of 3–4 hours or, for enhanced flavor, overnight.

Sear the Pork:

Preheat the oven to 350°F (175°C). Heat a skillet over medium-high heat until hot, then sear the pork on all sides for 2–3 minutes per side, forming a golden-brown crust.

Roast the Pork:

Transfer the seared pork to a greased roasting pan or baking dish. Bake for approximately 30 minutes or until the internal temperature reaches 160°F (71°C). Remove from the oven and let the meat rest for at least 5 minutes before slicing.

Prepare the Pan Sauce:

While the pork rests, return the skillet to medium heat. Pour in the chicken broth and use a wooden spoon to deglaze the pan, scraping up any browned bits. Add the reserved marinade and let it simmer for 2 minutes. Stir in the butter and brown sugar, allowing both to melt and integrate into the sauce.