Dry chicken with paper towel. Remove the bone with kitchen shears and trim any excess fat. Salt skin generously. Season meat side with about 1 tsp salt and 1 tsp white pepper. Heat a large pan over medium-high (cast iron is great for this). Put the chicken in the pan, skin-side down, then leave it alone – the fat needs to render for the skin to crisp up. Let skin side fry until crispy and golden brown, about 10-12 minutes; use a splatter guard to keep the oil from going all over the place. Flip chicken, cook an additional 3-5 minutes or more, until cooked through. Let drain on paper towels.
While the chicken rests, remove all but about 2 tbsp chicken fat from the pan and add garlic; sauté over medium heat until fragrant, about 1 minute. Add in the chili flakes and green onions and cook a couple more minutes. Season with 1 tsp white pepper and 1 tsp salt; taste and adjust seasoning as needed. Pour over crispy chicken thighs.