1 tablespoon olive oil
1 pork tenderloin
1/4 cup whole-grain mustard
2 tablespoons Dijon mustard
2 tablespoons sour cream
Heat the olive oil in a large straight-sided skillet over high heat. Season the pork with salt and pepper. Cook until browned on all sides, 5 to 6 minutes.
Reduce the heat to medium-low. Cover; cook, turning the pork occasionally, 20 to 25 minutes. Transfer pork to a plate, cover with foil, and let rest 10 minutes.
To the skillet, add both mustards, the sour cream, and any accumulated pork juices from the plate; whisk over medium heat until heated through. Add water to thin sauce to desired consistency. Slice the pork and serve with pan sauce.