Cut the pork tenderloin into medallions and gently flatten each piece using the side of a knife. Season both sides with salt and pepper.

Slice button mushrooms into thin slices.

Add the oil to the skillet and heat it over medium heat. Wait until the oil gets hot, then add seasoned pork medallions. Cook for about 3 minutes on one side, then flip and continue cooking until fully cooked through and lightly golden. Use cooking tongs to transfer the cooked pork medallions to a plate and set aside.

Add sliced button mushrooms to the skillet where you cooked pork medallions. Saute the mushrooms by stirring often until the water has been released and the mushrooms become pale brown.

Sprinkle the all-purpose flour over the mushrooms and continue sauteing them for 2 more minutes stirring frequently.

Season with salt, pepper, dried parsley flakes, and dried thyme. Stir to combine, then add the sour cream. Mix thoroughly until the sour cream is fully incorporated with the mushrooms. Let the sauce simmer for 4 to 6 minutes, stirring occasionally, until thickened.

Taste and adjust seasoning if needed. Using cooking tongs, gently return the cooked pork medallions to the skillet, and coat them in the sauce. Let them heat through for less than a minute, then remove from the stove. Serve no onion no garlic Pork Tenderloin in Creamy Mushroom Sauce with cooked gnocchi or pasta.