Step 1

Make sure the turkey is thawed; it will take about 1 day of refrigerator thawing time for every 4 pounds of turkey.

Step 2

Twenty-four hours or up to 3 days before roasting, remove any giblets and the neck from the cavity of the turkey (discard or save for making stock). If there is a plastic cage or pop-up thermometer in the turkey, remove and discard. Pat the turkey very dry inside and out with paper towels.

Step 3

Place the turkey breast-side down on a rimmed baking sheet. Use sharp kitchen shears to cut along each side of the backbone to remove it. Flip the turkey over, then use both palms to press down on the breast until you hear a crack and it flattens. (Here are some step-by-step photos.)

Step 4

Strip the leaves from 1 fresh rosemary sprig and finely chop (about 1 tablespoon). Season the turkey all over with 1 tablespoon plus 1 teaspoon kosher salt. Use your finger to gently loosen the skin on the breast, then rub the rosemary onto the breast meat. Cover the turkey loosely with plastic wrap and refrigerate at least 24 hours or up to 3 days.

Step 5

One hour before roasting, let the turkey sit at room temperature. Place 4 tablespoons unsalted butter or ghee in a small bowl and let sit out at room temperature to soften.

Step 6

Arrange a rack in the middle of the oven and heat the oven to 450ºF. Meanwhile, finely grate the zest of 1 large lime (about 1 heaping teaspoon) into the bowl of butter. Add 1 tablespoon white miso paste and smash and stir with a fork to combine.

Step 7

Peel and cut 1 medium red onion into 1-inch wedges and arrange on the baking sheet around the turkey (if liquid has pooled on the baking sheet, wipe it off first). Drizzle 3 tablespoons olive oil over the turkey, onion, and in the cavity of the turkey, then rub the oil over the turkey to evenly coat.

Step 8

Take a small spoonful of the miso butter, lift up the skin over one breast half, and tuck it under the skin. Repeat with the remaining breast half. Rub the remaining compound butter all over the skin covering the breast in an even layer with no clumps. If using the garlic, cut the top off 1 head to expose the cloves. Drizzle the cut side with olive oil and season with a little kosher salt. Place cut-side down on the baking sheet.

Step 9

Roast the turkey until the skin starts to darken and bubble, 25 to 30 minutes. If it looks like it’s burning or smoking, reduce the heat by 25 or 50 degrees. Spoon any juices on the baking sheet over the turkey and stir the onions. Rotate the baking sheet. Continue to roast until the skin is darkened and an instant-read thermometer inserted into the thickest part of the thigh not touching bone registers at least 165°F, 55 to 65 minutes more. If the wing tips look like they are burning at any point, cover with aluminum foil, shiny-side out, and return to the oven. (This is a good time to make the gravy if you haven’t already done so.)

Step 10

Let the turkey rest for at least 10 minutes before carving. Serve with the gravy and onions. Squeeze the caramelized garlic cloves out of their skins to eat with the meal or spread on bread.

Step 11

Thinly slice 1 small red onion (2 1/2 cups). Trim and thinly slice 1 pound cremini or mixed wild mushrooms (8 cups).

Step 12

Heat 1/4 cup olive oil in a large (about 12-inch) skillet over medium heat until shimmering. Add the onion, season with 1/4 teaspoon of the kosher salt, and cook, stirring occasionally, until starting to soften, about 4 minutes. Add the mushrooms, season with the remaining 1/2 teaspoon kosher salt, and cook, stirring every few minutes, until they have shrunken down and are silky and most of the liquid has evaporated, 10 to 12 minutes.

Step 13

Add 2 tablespoons unsalted butter or ghee and 1 tablespoon white miso paste and stir until melted. While stirring constantly with a wooden spoon and scraping up anything on the bottom of the pan, sprinkle in 1/2 cup all-purpose flour in about a tablespoon at a time. Continue stirring for 1 minute.

Step 14

While stirring constantly, pour in 1 (32-ounce) box vegetable broth a little at a time, and stir until the flour is dissolved. Bring to a simmer. Continue to simmer, stirring often, until thickened but still pourable, about 8 minutes more. Add 1 tablespoon low-sodium soy sauce and stir to combine. Remove from the heat. Taste and season with kosher salt and black pepper as needed.