For brine: Pour water, sugar and salt into a saucepan and bring to a boil. Once the sugar and salt dissolve, remove from heat and stir in the peppercorns, coriander seeds and sage. Place chicken in a large container. Add 3 cups ice to the hot brine and once the temperature comes down, pour over the chicken. Cover and refrigerate for at least 6 hours and up to 24 hours.
Remove chicken pieces from the brine and pat dry.
For chicken: In a shallow baking dish combine flour, baking soda, garlic powder, and salt and whisk together. Pour buttermilk into another shallow baking dish.
Dredge each piece of chicken into the flour mixture, shaking off any excess.
Next, dip each piece into the buttermilk followed by the flour mixture for a second coating. Place each dredged piece onto a parchment lined baking sheet.
Pour 3 inches fryer oil into a large cast iron skillet and preheat to 350˚F.
Once the oil is hot, place a few pieces of chicken into the oil, with about 1 inch of room between, making sure not to overcrowd the pan.
Fry each piece of chicken for about 10 to 12 minutes on each side or until golden brown and the chicken has an internal temp of 160˚F.
Remove chicken from the oil and transfer to a baking sheet lined with a cooling rack. Repeat until all of the chicken has been fried.
For sauce: Combine all ingredients together and whisk together until a thick and even paste forms.
Brush a thin coating of the paste onto each piece of fried chicken. Serve.