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1
Preheat oven to 350 degrees F (175 degrees C).
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2
Rub salt and pepper over all sides of pork tenderloins; nestle tenderloins next to each other in a 9x13-inch baking dish.
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3
Melt butter in a saucepan over medium heat; add garlic and mushrooms. Bring to a boil, reduce heat to medium-low, and simmer, stirring frequently, until sauce is fragrant, about 5 minutes. Stir vinegar into mushroom sauce. Pour mushroom sauce over tenderloins, letting sauce seep between the two tenderloins.
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4
Bake in the preheated oven until tenderloins are lightly pink in the center, about 45 minutes. An instant-read thermometer inserted into the center should read at least 145 degrees F (63 degrees C). Transfer tenderloins to a serving dish.
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5
Drain the drippings, including mushrooms, from the baking dish into a measuring cup, scraping the bottom to get all the brown bits. Remove 1/4 cup of the fat from the mixture and pour into a saucepan. Add enough chicken broth to the drippings to make 2 cups; whisk flour into drippings until incorporated. Stir broth-drippings mixture into the saucepan with fat over medium heat until thickened, about 5 minutes; season with salt and pepper.
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6
Slice tenderloins into medallions and top with half the gravy. Pour the remaining gravy into a gravy boat for serving.
