Place a rack in the center of the oven. Preheat the oven to 350°F.
Grate the zest from 1½ tangerines, or enough to make 1 tablespoon. Squeeze 1 tangerine to get 1/3 cup juice. Set aside.
Slice the thickest part of the parsnips lengthwise into quarters or halves so that they are the same thickness as the thinner halves.
Put the butter in a 12 × 10 × 2-inch roasting pan. Place the pan in the oven for 1 minute to melt the butter. Remove from the oven. Toss the parsnips in the pan, turning to coat evenly with butter. Spread out in a single layer.
Combine the stock, zest, juice, vinegar, salt and just a touch of pepper. Pour over the parsnips. Bake for 40 minutes, turning the vegetable over every 10 minutes.
Bake for about 20 minutes more without turning the parsnips. The parsnips will be tender and the sauce reduced to a glaze.
Nutritional information is based on 5 servings, but does not include Basic Chicken Stock. For nutritional information on Basic Chicken Stock, please follow the link above.