1. Marinate the chicken by placing chicken breasts or thighs in a large bowl or zip-top bag, pouring enough buttermilk to submerge the chicken fully, and adding kosher salt, black pepper, garlic powder, onion powder, and ground ginger. Mix well, cover, and refrigerate for at least 2 hours or overnight.
2. Prepare the Gochujang Mayo by combining mayonnaise and gochujang paste in a small bowl. Add optional lime or lemon juice, fine sea salt, and ground black pepper for extra flavor. Mix until well blended and refrigerate.
3. Make the spicy Gochujang Sauce by combining gochujang paste, ketchup, mirin, soy sauce, honey, brown sugar, minced garlic, and grated ginger in a saucepan. Simmer over medium heat for 5-7 minutes until thickened, then set aside.
4. Coat the marinated chicken by mixing all-purpose flour with salt, pepper, garlic powder, and onion powder in a shallow dish. Remove excess buttermilk from the chicken, dredge in the flour mixture, and press firmly for an even coating.
5. Heat vegetable oil in a deep fryer or large skillet to 350°F. Fry the chicken in batches for 6-8 minutes per side, ensuring it is golden brown and cooked through. For additional crispiness, cool slightly and double-fry at 375°F for 2-3 minutes. Place on a wire rack or paper towel to drain excess oil.
6. Prepare accompaniments like pickled slaw by mixing shredded cabbage, grated carrots, rice wine vinegar, sugar, and salt, or use kimchi slaw for a Korean-inspired side.
7. Assemble the dish by spreading gochujang mayo on a toasted brioche bun if serving as a sandwich. Add the crunchy fried chicken, drizzle with the spicy gochujang sauce, and layer with pickled slaw or kimchi slaw. Serve immediately.
8. Maintain oil temperature with a thermometer while frying for consistent results. Keep fried chicken warm in a 200°F oven for batch preparation.
9. For gluten-free or vegetarian alternatives, use rice flour or tofu/cauliflower instead of chicken, following the same preparation process.
10. Store leftovers by cooling fried chicken completely, placing it in an airtight container with paper towels, and refrigerating for up to 3 days. Reheat in a 375°F oven for 10-15 minutes to restore crispiness.
11. Keep leftover gochujang mayo in an airtight container in the refrigerator for up to one week. Stir before use to combine separated ingredients.