Combine the mustard, garlic, rosemary, and black pepper in a small bowl; stir well, and set aside.
Slice the tenderloins lengthwise to, but not through the center, leaving one long side connected. Spread the mustard mixture evenly into the opening of each tenderloin. Fold the top sides over the mustard mixture, and tie securely with string at 2 inch intervals.
Place the tenderloins, seam side down, on a lightly greased rack in a roasting pan. Brush each with 1 tbsp marmalade. Add water to the pan. Bake uncovered, at 400 degrees for 35 minutes or until a meat thermometer inserted in the thickest part of the tenderloins registers 160 degrees. (medium).
Combine the remaining 2 tbsp marmalade and chicken broth in a small saucepan. Bring to a boil; reduce heat and simmer; uncovered for 2 to 3 minutes or until thickened.
To serve, slice the tenderloins, and arrange on a serving platter. Spoon the marmalade mixture over the slices.