Pat the halal turkey roast completely dry with paper towels. Mix garlic powder, onion powder, dried thyme, sage, 1 teaspoon sea salt, and black pepper in a small bowl. Rub the seasoning blend thoroughly over all sides of the turkey.

Heat 2 tablespoons olive oil and 1 tablespoon butter in a large heavy Dutch oven or braiser over medium-high heat. Sear the turkey roast for 4-5 minutes per side until skin is golden brown and caramelized. Transfer to a plate.

Add the chopped onions, celery, and smashed garlic to the pot. Sauté for 3 minutes until fragrant, scraping up any browned bits with a wooden spoon.

Pour in 2 cups of halal chicken bone broth to deglaze the pot. Scatter the halved baby Yukon potatoes and baby carrots evenly across the bottom of the Dutch oven.

Nestle the seared turkey roast on top of the bed of vegetables. Dot the turkey with the remaining 2 tablespoons of butter and tuck fresh rosemary and thyme sprigs around the pot.

Cover tightly with the lid. Transfer to a 325°F (165°C) oven (or cook on LOW in a slow cooker for 6 hours) and braise for 75-90 minutes until the turkey registers 165°F (74°C) on an instant-read meat thermometer and root vegetables are fork-tender.

Carefully transfer the turkey and vegetables to a warm serving platter and tent with foil to rest for 10 minutes.

Place the Dutch oven with the remaining braising liquid over medium heat on the stove. Whisk in a flour or cornstarch slurry (2 tbsp flour mixed with 3 tbsp cold broth) and simmer for 3-4 minutes until rich, glossy, and thickened into a velvety herb gravy. Carve juicy turkey into thick slices and ladle gravy generously over top. Serve immediately!