In a small bowl or large measuring cup, whisk together 1 1/2 cups buttermilk, 1 tablespoon garlic powder, 1 tablespoon dried Italian seasonings, 1 teaspoon ground red pepper, and 2 teaspoons coarse salt.
Pour the buttermilk mixture into a large zip-top plastic bag or a baking dish. Add 3 pounds of bone-in chicken pieces. Toss to coat, seal or cover, and refrigerate for at least 2 hours, up to overnight, turning occasionally.
Remove the chicken from the refrigerator 30 minutes before cooking to bring it to room temperature. Discard the used marinade.
For grilling: Preheat the grill to medium-low heat. Place the chicken on the grill, cover, and cook for 30-40 minutes, turning occasionally, until golden brown and internal temperature reaches 165°F (74°C).
For baking: Preheat the oven to 450°F (232°C). Arrange the chicken in a single layer in an oven-safe skillet or baking pan. Bake for about 30 minutes, until internal temperature reaches 165°F (74°C).
Let the chicken rest for 5 minutes before serving to lock in juices. Serve hot with your choice of sides.