Make the Spice Rub: whisk together salt, paprika, onion powder, garlic powder, chili powder, black pepper, dried crushed oregano, dried basil, and 1 teaspoon ground red cayenne pepper in a small bowl.
Reserve portions of the rub: remove 1 1/2 tablespoons of the Spice Rub and combine it with 2 cups buttermilk and 2 bay leaves in a large bowl; add the chicken and toss to coat. Cover and refrigerate 3 hours or up to overnight.
When ready to cook, set aside 1 teaspoon of the Spice Rub in a medium bowl for the Nashville Hot Sauce and combine it with 2 tablespoons hot sauce, 1 tablespoon ground red cayenne pepper, 2 tablespoons brown sugar, 1/2 teaspoon smoked paprika, and 3/4 cup vegetable oil; whisk until combined but wait to add melted butter.
Prepare the buttermilk egg wash: whisk 2 eggs with 1 cup buttermilk and 1/4 cup hot sauce in a medium bowl.
Make the flour breading: whisk 3 1/2 cups all-purpose flour with 1 tablespoon baking powder and the remaining Spice Rub in a large bowl.
Coat the chicken: working one piece at a time, dredge chicken in the flour mixture and shake off excess, dip into the buttermilk egg wash, shake off excess, then dredge again in the flour. Place coated pieces on a baking rack and repeat with remaining chicken.
Heat the frying oil: add vegetable oil to a Dutch oven or large pot to a depth of about 3 inches and heat over medium-high until it registers 375°F (190°C) on a thermometer.
Fry the chicken: fry 3–4 pieces at a time in a single layer. Cover and cook 7 minutes, flip, cover and continue frying until internal temperature reaches 165°F for dark meat (160–165°F for white), about 5–7 more minutes depending on piece size.
Drain: transfer fried chicken to a paper towel–lined baking sheet to drain while you finish frying the rest.
Finish the Nashville Hot Sauce: vigorously whisk the melted butter into the prepared hot sauce until smooth.
Brush and serve: let the chicken cool slightly, then brush each piece with the desired amount of Nashville Hot Sauce; adjust amount for spiciness.