For marinade, combine ingredients. Put the pork into a large baggie and pour marinade in. Marinate pork, refrigerated, overnight or as long as you want, turning the bag over occasionally.
Mustard Sauce
For mustard sauce, combine ingredients and refrigerate at least 2 hours.
Grill pork tenderloin 15 to 20 minutes, turning occasionally. Or, if you like, broil it. Cook until most of the pink is gone. If using a thermometer, tenderloin should cook to 160°F–165°F. Slice in thin slices diagonally. Serve with mustard sauce. Makes about 4 to 8 servings. If desired, serve in buns as sandwiches.