Marinate the chicken. In a high-powered blender, combine the buttermilk, lemongrass, thai chilies, fish sauce, egg, and 1 tablespoon of kosher salt. Place the chicken in a large ziplock bag and pour the buttermilk marinade over the chicken. Seal the bag, pressing as much of the air out of the bag as possible, and let the chicken marinate overnight.
Make the honey chili crisp. Add the chili oil to a small saute pan or pot over medium heat. Add white and light green parts of green onion and cook for 2-3 minutes until softened. Add honey, ginger and garlic. Cook for 2 more minutes, just until the garlic is no longer raw. Stir in the sliced dark green parts of the scallion. Set aside.
Dredge the chicken. Remove the chicken from the fridge 1 hour before cooking. In a shallow dish, combine the flour, baking powder, cornstarch, white pepper, and 1 tablespoon of kosher salt. Whisk the flour mixture well so that everything is evenly distributed. Remove the chicken from the marinade, shaking off any excess, and coat the pieces really well in the flour, pressing the flour into the meat. Transfer the chicken to a wire rack set over a baking sheet and let it rest for 10-15 minutes before frying.
Fry the chicken pieces. Heat about 3 inches of oil in a large dutch oven or pot over medium-high heat until the temperature reaches 350 F. Lower the heat to medium. Working in batches of 3-4 pieces of chicken at a time, fry the chicken for 8-12 minutes, keeping the heat steady, until the chicken reaches an internal temperature of 165 F. Use a spider to transfer the chicken to a wire rack set over a baking sheet. You can keep the chicken in a 200 F oven to keep it warm while you fry the rest of the chicken.
Drizzle the fried chicken with the honey chili-crisp and serve with the charred scallion ranch on the side.