Place the chicken pieces in a bowl and pour 1/2 cup buttermilk over them; toss to coat and let sit while you prepare the coating.
Preheat the oven to 425°F (218°C) and line a baking sheet with parchment paper.
In a medium bowl combine the crushed corn flakes, paprika, and a pinch of kosher salt and black pepper; stir to mix evenly.
Working one piece at a time, lift the chicken from the buttermilk, let excess drip off, then press into the corn flake mixture to coat fully; place coated pieces on the prepared baking sheet without crowding (use a second sheet if needed).
Lightly drizzle or brush the coated chicken with olive oil, then bake for 15–20 minutes, until the chicken is cooked through and coating is crisp.
While the chicken bakes, whisk together 3/4 cup BBQ sauce, 1/4 cup honey, 2 tablespoons Dijon mustard, and 1/2 teaspoon cayenne in a jar or bowl until smooth.
Remove the chicken from the oven, drizzle or brush each piece with the honey-BBQ sauce, then return to the oven for about 5 minutes to warm the sauce.
To make the spicy ranch, combine 1 cup plain Greek yogurt, 1/2 cup buttermilk, 1 tablespoon dried parsley, 2 teaspoons dried dill, 1 teaspoon garlic powder, 1 teaspoon onion powder, 1 teaspoon kosher salt, the chopped jalapeño, and 2 tablespoons chopped fresh chives in a jar; shake or stir until creamy.
Serve the baked honey-BBQ chicken topped with additional chopped chives and the spicy ranch on the side for dipping.