In a large pot, combine 1 cup kosher salt, 1/2 cup brown sugar, bay leaves, peppercorns, crushed garlic, rosemary and thyme sprigs with 1 quart of water. Heat just until salt and sugar dissolve, then remove from heat and add remaining 2 quarts cold water to cool the brine to room temperature.

Brine the turkey

Remove giblets and neck from turkey cavity. Place the 12 lb turkey in a large brining container or a heavy-duty resealable bag. Pour cooled brine over the turkey, ensuring it is fully submerged (use a weight if needed). Refrigerate or keep in an ice chest at 40°F (4°C) for 8–12 hours. After brining, discard brine, rinse turkey thoroughly under cold water, and pat dry with paper towels inside and out.

Seasoning & Fat

Make herb butter

In a bowl, combine 3/4 cup softened unsalted butter, 2 tablespoons olive oil, minced garlic, lemon zest (from 1 lemon), chopped sage, rosemary and thyme, 2 tsp salt and 1 tsp black pepper. Mix until smooth and well blended.

Apply butter under skin and on surface

Loosen the skin over each turkey breast gently with your fingers by inserting them between skin and meat without tearing. Spread about two-thirds of the herb butter evenly under the skin over the breast meat. Rub remaining butter over the outside of the turkey to help browning. Tuck wing tips under the bird.

Aromatics for Cavity & Roasting Pan

Fill cavity and prepare roasting pan

Stuff the turkey cavity loosely with quartered onion, celery pieces, carrot, halved lemon, rosemary and thyme sprigs. Place a rack in a large roasting pan and add the remaining onion/celery/carrot pieces to the bottom of the pan to create a flavor base. Pour 2 cups of chicken or turkey stock into the bottom of the pan (this will keep drippings from burning and produce pan juices for gravy).

Roasting & Finishing

Truss and preheat

If desired, truss the legs with kitchen twine to ensure even cooking. Preheat the oven to 325°F (163°C). Position the oven rack in the lowest third of the oven to accommodate the bird.

Initial roast

Place the prepared turkey breast-side up on the rack. Roast at 325°F. General guideline: roast about 13 minutes per pound for an unstuffed turkey, so for a 12 lb all-white-meat bird plan ~2 hours 35 minutes, but start checking early. Baste gently with pan juices every 30–40 minutes if desired.

Shielding and temperature check

If breast skin is getting too dark, tent loosely with foil. Begin checking internal temperature after about 2 hours. Insert an instant-read thermometer into the thickest part of the breast without touching bone. The turkey is done when breast reaches 165°F (74°C). For all-white meat, aim for 165°F and then remove from oven promptly to avoid overcooking.

Resting

Transfer the turkey to a cutting board and tent loosely with foil. Let rest 20–30 minutes before carving. Reserve pan drippings for gravy or serving.

Finishing / Optional

Carve and serve

Un-tie the twine if used. Carve the turkey, portioning breast meat into slices. Serve with pan juices or prepared gravy made from the drippings.