In a small, heavy, non-reactive stockpot, add the lemon juice and 6 cups of water. Peel, core and quarter the quince, and peel the parsnips and cut into 1/2-inch slices, then place in the lemon water to prevent discoloration. Bring the quince, parsnips, lemon water, 2 tablespoons sugar, and cinnamon sticks to a boil over high heat, and gently boil until very tender, about 20 - 30 minutes.
Remove the fruit with a slotted spoon to the bowl of a food processor, and in batches, process with 3 tablespoons reserved cooking liquid, heavy cream, butter, remaining 2 tablespoons sugar, salt, remaining 1/2 teaspoon lemon juice and allspice until very smooth.
Place the pork tenderloins in a large non-reactive pan. In a mixing bowl combine all remaining ingredients except salt and pepper and pour over the pork tenderloin, turning over to coat both sides. Cover the pork tightly and marinate in the refrigerator for at least 2 hours, and up to 12 hours.
Preheat oven to 400ºF and remove the pork tenderloins from the marinade. Season pork with salt and pepper and sear on all sides in a hot, ovenproof skillet over high heat. Transfer to oven and cook to an internal temperature of 150ºF., about 12 to 15 minutes. Let rest for 5 minutes before serving with Quince Puree and Port Wine Reduction.
Yield: 4 to 6 servings
PORT WINE REDUCTION:
One 750 ml bottle Ruby Port wine (4 cups)
In a large heavy saucepan, bring the Port to a boil over high heat. Continue cooking at a low boil until the wine thickens and reduces to a syrup measuring 1/3 cup, about 20 minutes.