How to Make It
Marinate the chicken: Combine the buttermilk, onion powder, pepper, salt, and cayenne in a large glass mixing bowl or ziptop bag. Add the chicken and submerge to coat completely. Cover and refrigerate for 12 hours and up to overnight.
Make the waffles: Preheat the oven to 250°F. In a medium saucepan, warm ¼ cup of milk with the ¼ teaspoon sugar over low heat for 2 minutes. Remove from the heat, add the yeast, and let it bloom until it foams, 15 minutes.
Add the remaining sugar, the melted butter, and egg yolks to the milk-yeast mixture and whisk to combine. Whisk in the flour, alternating with the remaining 2 ½ cups of milk, until smooth. In a stand mixer fitted with the whisk attachment, whip the egg whites until they form stiff peaks, 3 minutes on high speed, then fold them into the waffle batter.
Grease a waffle iron with butter and cook the waffles, ½ cup batter at a time, according to the manufacturer’s instructions. Keep the waffles warm on a sheet pan in the oven while you fry the chicken.
Fry the chicken: Fill a cast-iron skillet with 1½ inches of oil and heat to 350°F.
In a medium mixing bowl, whisk the flour, onion powder, pepper, salt, and cayenne. Place the buttermilk in a separate bowl. Remove the chicken from the marinade, letting the excess drip off. Coat the chicken in the flour mixture first, then the buttermilk, then the flour mixture again, shaking off the excess at each step.
Working in batches, fry the chicken until golden brown and cooked through (until a thermometer reaches 165°F when inserted into the thickest part), turning once, 7 to 8 minutes, letting oil return to temperature between batches. Transfer to a plate and keep warm in the oven between batches. Serve immediately with bacon and maple syrup.