1. Marinate chicken thighs in milk, gochugaru, salt and kimchi juice only. Let chicken thighs sit for at least 6 hours or overnight.
2. In a shallow bowl, add all-purpose flour, salt and black pepper and mix thoroughly. Remove chicken from wet mixture and dredge in seasoned flour. Tap against bowl to shake off excess.
3. Pour oil into a 10”-12” cast-iron skillet or other heavy straight-sided skillet (not nonstick) to a depth of ¾”.
4. Prop deep-fry thermometer in oil, so bulb is submerged. Heat over medium-high heat until thermometer registers 350F.
5. Place chicken thighs in skillet. Fry chicken thighs turning every 1–2 minutes and adjusting heat to maintain a steady temperature of 300F–325F, until skin is deep golden brown. Use an instant-read thermometer inserted into thickest part of chicken registers at 165F. Fry for about 10 minutes. 
6. Remove chicken thighs from skillet and shake off extra oil back into skillet. Transfer chicken thighs to serving dish.
7. Garnish chicken thighs with chopped wonbok kimchi.

Air Fryer Option:

1. Marinate chicken thighs in milk, gochugaru, salt, and kimchi juice only. Let chicken thighs sit for at least 6 hours or overnight.
2. In a shallow bowl, add all-purpose flour, salt and black pepper and mix thoroughly. Remove chicken from wet mixture and dredge in seasoned flour. Tap against bowl to shake off excess.
3. Place coated chicken thighs in air fryer basket, working in batches as necessary to not overcrowd the basket.
4. Cook at 400F until chicken thighs is golden brown. Use an instant-read thermometer inserted into thickest part of chicken registers at 165F. 20 to 25 minutes flipping halfway through.
5. Garnish chicken thighs with chopped wonbok kimchi.