You can brine your turkey up to 24 hours. So, make sure that you leave yourself plenty of time. This recipe is for a 18 to 20 pound turkey.
3 cups coarse salt
5 cups of sugar
2 medium onions, coarsely chopped
2 carrots, peeled and coarsely chopped
2 celery stalks, coarsely chopped
2 dried bay leaves
3 sprigs of fresh thyme
3 sprigs of fresh flat-leaf parsley
2 tsp of whole black peppercorns
Put salt, sugar, onions, carrots, celery, bay leaves, fresh thyme, parsley, peppercorns and 10 cups of water in a large stockpot. Bring to a boil, stirring until salt and sugar have dissolved. Remove from heat; let brine cool completely.
Add turkey, breast first, to the brine. Cover; refrigerate 24 hours. Remove from brine; pat dry with paper towels. Let stand at room temperature for 2 hours.