Sprinkle the garlic and pepper over the tenderloin(s), then melt your butter in a pan. When it's nice and hot, quickly sear the tenderloin on all sides.
Open your red wine and pour yourself a glass. Place your seared roast(s) in a baking pan or skillet. Place the mushrooms around the tenderloin in the pan.
Mix the wine, beef broth, and gravy mix together.
Pour the red wine mix over the pork.
Place in the oven and cook until the internal temperature reaches 145 °F.
Pull it out of the oven and remove the roast(s). Cover it on the plate with foil to keep the heat in.
Pour the remaining sauce into a pot to make a gravy. You can bring it to a boil and boil off the excess liquid to thicken, or you can make a cornstarch slurry. Whisk together the slurry ingredients and then whisk into the gravy to thicken, Cook for a few minutes until thickened, then remove.
Slice the tenderloin then serve with the gravy.
You can use 1-3 tenderloins in this recipe, just sprinkle them all with pepper and garlic, and sear. Cook them together in the pan.