In a large mixing bowl, combine the buttermilk, flour, cornstarch, egg, hot sauce, and a generous pinch of salt and pepper. Whisk until smooth to form the buttermilk mixture.
Take the chicken chunks and, one by one, dip them into the buttermilk mixture. Ensure each piece is thoroughly coated, then press them into the Panko breadcrumbs, making sure the breadcrumbs adhere well.
In a large pot or Dutch oven, pour in the vegetable oil and heat over medium-high until it reaches 360°F on a deep-fry thermometer. This temperature ensures a perfect fry.
Once the oil is ready, carefully lower the chicken pieces into the pot in small batches, frying them for 2 to 3 minutes, or until they turn a rich, golden brown and achieve a crisp outer layer. After frying, transfer the chicken onto a plate lined with paper towels to drain any excess oil.
Serve the crispy chicken immediately, drizzling with the sweet chili sauce and garnishing with fresh parsley for added flavor and presentation.