Probably the trickiest part of roasting a turkey is being sure the breast and thigh meat are done at the same time. All too often, the breast meat ends up dry and overcooked while you are waiting for the thighs to finish cooking. Any one of these techniques will help prevent the breast from overcooking:
For an unstuffed turkey, roast the turkey, breast side down, for the first one-third of the cooking time. This increases the rate at which the thighs cook, so they will be done at about the same time as the breast.
For a stuffed turkey, loosely cover the breast with a double-thick piece of aluminum foil for the first two-thirds of the cooking time. This slows the rate at which the breast cooks, so it will be done at about the same time as the thighs.
Checking the Internal Temperature
The breast and thighs must reach different internal temperatures for ideal doneness. The breast should register 165°F and the thigh, 175°F. Begin testing for doneness about 30 minutes before the total roasting time is reached.
The turkey will continue to cook internally after you remove it from the oven, so you may take it out when the thermometer registers 3° to 4°F below the minimum temperature. Then cover the bird loosely with aluminum foil.
If roasting a stuffed bird, be sure the stuffing reaches 165°F.
To test the breast:
Using an instant-read thermometer, insert it into the meatiest part, several inches above the wings.
To test the thigh:
Insert the instant-read thermometer away from the bone, alongside the opening of the main cavity underneath the drumstick. This is the meatiest part of the thigh.