Spicy Chipotle Chicken Tostadas

Fill a large pot with 8 cups water; stir in 1/4 cup salt. Add chicken and simmer over medium-low heat until just cooked through, about 45 minutes. Drain, then chop or tear chicken into bite-size chunks. Discard bones. Meanwhile, purée tomatoes, chiles, adobo sauce, pepper, cinnamon, and cloves in a blender until smooth. Cook onion in a large skillet over medium-high heat, stirring occasionally, until sweet and charred (you want more char than "caramelization"), 8 –10 minutes. Add garlic and cook, stirring occasionally, until golden brown and fragrant, about 3 minutes longer. Add tomato mixture to skillet (it will splatter), reduce heat, and simmer, partially covered, about 30 minutes. Add chicken and chorizo, if using, and cook, stirring occasionally, until chicken is well-coated and moist and liquid is reduced and thickened, about 10 minutes more. Season with salt, if needed.