Step 1Place the tenderloin in a large plastic food bag. Combine the garlic, shallot, mustard, vinegar, oil, herbs, 1 teaspoon of salt and the pepper in a small dish. Add to the meat. Work through the bag to coat the meat. Tightly seal the bag to keep all the meat covered in the marinade. Place the bag in a bowl. Refrigerate the meat overnight, turning the bag occasionally. Let the meat come to room temperature before grilling.
Step 2Prepare a medium-hot barbecue fire with a few chunks of water-soaked wood. Alternatively, place the broiler rack 8 inches from the heat source; heat to medium-high heat. Drain the meat; reserve the marinade. Lightly sprinkle the meat with more salt.
Step 3Grill or broil the tenderloin until cooked as desired, brushing with the reserved marinade and turning as necessary. Depending on the heat, it may take as long as 15 to 20 minutes to cook the meat; an instant-read thermometer should register 125 degrees for medium rare, 130 degrees for medium. Tent loosely with foil; let the meat rest at least 10 minutes before slicing and serving.
Step 4Serve the meat hot or at room temperature. Cut it into thin slices close to serving time. Arrange the marmalade on a platter. Overlap the tenderloin slices attractively on the marmalade. Spoon accumulated pan juices over the meat. Garnish the platter with herb sprigs.