To make the marinade for the turkey: Place the onion, garlic, mustard, and Worcestershire sauce in a food processor and puree until completely blended. Put the turkey in a roasting pan fitted with a rack. Rub the outside of the turkey all over with the mustard mixture. Cover the turkey with plastic wrap to keep in the moisture. Refrigerate the turkey overnight or up to 24 hours.
Preheat the oven to 400 degrees F.
Remove the turkey from the refrigerator and discard the plastic wrap and place in a roasting pan. Tuck the turkey wings beneath the breast and tie the base of the legs together with butcher's twine. Using a pastry brush or bulb baster, baste the turkey with some of the malt. Transfer the turkey to the oven and roast, uncovered, for 3 hours, basting every 30 minutes with the malt. If the turkey breast starts to look like it's getting too dark, cover it with aluminum foil.
Cook until the juices run clear and the turkey's internal temperature is 160 degrees F in the breast and the leg registers 175 degrees F on an instant-read thermometer.
Remove the turkey from the oven and cover it loosely with foil. Let the turkey rest for 30 minutes before carving and serving with the stuffing and cranberry passion fruit sauce on the side.