Unwrap the turkey and remove the neck and giblets (reserve for gravy). Rinse the turkey under cold water and pat dry. Fill a large pot with 2 quarts water; add 2 cups kosher salt, the brown sugar, juniper berries, peppercorns, bay leaves and lemon zest. Bring to a boil, then simmer 10 minutes. Add 6 quarts cold water and let cool. Submerge the turkey in the brine, adding water to cover, if necessary. Refrigerate at least 8 hours or overnight.
Remove the turkey from the brine; rinse and pat dry. Crush and chop the coriander seeds, cumin seeds and garlic. Mix with the paprika and butter until combined. Reserve 4 tablespoons of the butter, then rub the rest under the turkey skin on the breasts and legs. Rub 2 tablespoons of the reserved butter on the skin; chill and save the rest for your gravy. Let the turkey stand 30 minutes at room temperature before roasting.
Put the oven rack in the lowest position; preheat the oven to 350 degrees F. Put the turkey breast-side up on a rack in a large roasting pan, tucking the wing tips under. Tie the drumsticks together with twine. Roast until the skin is golden brown and a thermometer inserted into the thigh registers 165 degrees F, about 15 minutes per pound. Transfer to a cutting board and let rest 30 minutes before carving. Whisk the reserved 2 tablespoons flavored butter into your gravy just before serving, if desired.
This recipe is not for a Kosher Bird, which is already brined. Use only for a frozen or fresh bird.