I found this in my cooking folder as a hand-scratched note one night as I was trying to find a half decent tenderloin recipe. Result was a decent sauce and a very juicy tenderloin.

Ingredients

2-3 pounds pre-marinated tenderloin (black pepper flavor works)
1 tablespoon butter
1 teaspoon pepper
1 cup red wine
1 cup beef broth
1 cup sliced white mushrooms
corntarch (standby)
cold water (standby)

Instructions

Preheat oven to 350 °F .

Melt butter in a cast-iron pan. When hot, sear the tenderloin on all sides.

Place the mushrooms around the tenderloin in the pan.

Mix the wine and beef broth together, and pour the mix over the pork.

Put pan in the oven and cook until the internal temperature reaches 145-150 °F.

Pull it out of the oven and remove the pork to a cutting board.

Place the pan with the wine/stock mix on a stove burner and bring to medium boil. Let reduce for a few minutes. If the thickness needs to be increased, use a little cornstarch and water to make a slurry, and add to the pan. Heat until slightly thickened but not thick.