Preheat the oven to 400°F.
Combine the garlic powder, dried thyme, lightly crushed rosemary, oregano, salt, and black pepper in a small bowl. Stir until the seasonings are evenly distributed to create the dry rub.
Blot both pork tenderloins thoroughly with paper towels to remove excess surface moisture.
Coat the pork evenly with 2 tablespoons of olive oil. Sprinkle the prepared seasoning mixture over every side of the tenderloins, gently pressing the herbs and spices against the meat so they adhere well.
Place a cast-iron skillet over medium-high heat and add 1 tablespoon of olive oil.
When the oil is hot, place the seasoned pork tenderloins in the skillet. Sear the first side for approximately 1 minute, or until a golden-brown crust develops.
Turn the pork and continue searing each remaining side until the exterior is evenly browned. This should require only a few additional minutes.
Transfer the skillet containing the seared tenderloins directly into the preheated oven.
Roast for approximately 20 minutes, turning the pork over halfway through the cooking period.
Insert a meat thermometer into the thickest section of the tenderloin. The internal temperature should reach 145°F. If necessary, continue roasting and check the temperature again every few minutes.
Once the pork reaches the proper temperature, remove the skillet from the oven and transfer the tenderloins to a plate.
Loosely cover the meat with aluminum foil and allow it to rest for 5 minutes before slicing. Resting helps preserve the pork's moisture and tenderness.
Return the skillet containing the pork drippings to the stovetop and set it over medium heat.
Add the unsalted butter and allow it to melt. As it melts, scrape the browned bits from the bottom of the skillet and incorporate them into the mixture.
Stir in the all-purpose flour until it is thoroughly combined with the butter, drippings, and remaining herbs.
Gradually add the 2% milk while whisking continuously to maintain a smooth consistency and prevent lumps.
Bring the mixture to a boil, then allow it to simmer until the gravy becomes smooth and thickened. Add a little additional milk when necessary to achieve the preferred consistency.
Remove the finished gravy from the heat.
Cut the rested pork tenderloins into slices and arrange them on serving plates.
Spoon the warm pan gravy generously over the pork, then finish with finely chopped fresh parsley for fresh flavor and color.