Add the chicken to a large bowl. Put the kimchi in a food processer and blend until smooth. Add it to the chicken along with the buttermilk and stir until well combined. Cover with plastic wrap and refrigerate for at least 8 hours and up to overnight.
When you are ready to cook the chicken, whisk the flour, chili powder, garlic powder, onion powder, smoked paprika, celery seeds, cumin and white pepper in a large bowl.
Working with one piece of chicken at a time, remove from the kimchi marinade, allowing any excess marinade to drip off, then dredge in the seasoned flour. Transfer the chicken to a wire rack set over a baking sheet. Repeat this process until all the chicken has been dredged once. Then dredge the chicken one piece at a time for a second time. This second dredge will make for an extra thick and crunchy crust. Repeat until all the chicken has been dredged twice. Let the chicken sit at room temperature while you heat up the oil.
Fill a large high-sided skillet or cast-iron pan with a little more than 1/2-inch of oil and heat to 375 degrees F on a deep-fry thermometer. When the oil is hot, fry the chicken in batches of 4 pieces until golden brown and the internal temperature is 165 degrees F on an instant-read thermometer, 6 to 8 minutes total, carefully turning the chicken once halfway through the cooking time. Transfer the fried chicken to a second wire rack set over a baking sheet. Allow the oil to return to 375 degrees F in between each batch.
Sprinkle the chicken with sliced scallions and serve immediately.