Ingredients

• 2 medium onions, chopped
• 8 large garlic cloves, chopped
• 1/3 cup plus 2 teaspoons salt
• 2 tablespoons black pepper
• 1 tablespoon cayenne
• 8 cups water
• 8 chicken breast halves, 8 drumsticks, and 8 thighs (all with skin and bones; 8 to 9 lb total)
• 10 cups all-purpose flour
• About 8 cups vegetable oil (64 fl oz)
• Special equipment: a wide 5- to 6-qt heavy pot (preferably cast-iron; 10 inches wide and 4 inches deep); a deep-fat thermometer

Instructions

1. Purée onions and garlic with 1/3 cup salt, 1 tablespoon black pepper, cayenne, and 1 cup water in a food processor until smooth, then pour into a large bowl and stir in remaining 7 cups water. Divide chicken and marinade among 3 (1-gallon) sealable plastic bags, then seal, forcing out excess air. Marinate chicken, chilled, turning bags over a few times, at least 12 hours. (If you're concerned about leaks, put bags in a large bowl.)
2. Dredge and fry chicken: Whisk together flour, remaining 2 teaspoons salt, and remaining tablespoon black pepper in a large bowl, then divide between 2 large roasting pans. Drain chicken in a colander, discarding marinade, then dredge each piece of chicken in seasoned flour and leave sitting in flour. Let chicken stand 20 minutes. Preheat oven to 250°F. Line 2 large baking sheets with paper towels and set a cooling rack on each. Heat 2 inches oil in pot over moderately high heat until it registers 365°F on thermometer. Knocking off excess flour, transfer 4 pieces chicken to oil (keeping batches all white meat or all dark) and fry, turning occasionally with tongs, until golden brown and cooked through, about 8 minutes for breasts or 10 to 12 minutes for drumsticks and thighs. Lift chicken from oil with tongs, letting excess oil drip back into pot, then transfer to a rack and keep warm in oven. Dredge and fry remaining chicken in same manner, keeping it warm in oven. (Return oil to 365°F between batches.)
3. Whisk together flour, remaining 2 teaspoons salt, and remaining tablespoon black pepper in a large bowl, then divide between 2 large roasting pans. Drain chicken in a colander, discarding marinade, then dredge each piece of chicken in seasoned flour and leave sitting in flour. Let chicken stand 20 minutes.
4. Preheat oven to 250°F. Line 2 large baking sheets with paper towels and set a cooling rack on each.
5. Heat 2 inches oil in pot over moderately high heat until it registers 365°F on thermometer. Knocking off excess flour, transfer 4 pieces chicken to oil (keeping batches all white meat or all dark) and fry, turning occasionally with tongs, until golden brown and cooked through, about 8 minutes for breasts or 10 to 12 minutes for drumsticks and thighs. Lift chicken from oil with tongs, letting excess oil drip back into pot, then transfer to a rack and keep warm in oven. Dredge and fry remaining chicken in same manner, keeping it warm in oven. (Return oil to 365°F between batches.)