Can do either, or both. If you want to use the buttermilk as a marinade, bring some up to 60/70 degrees, and add something to infuse (chilli, ginger, lemongrass, shallot?), then cool fully, put into the rest of the buttermilk, and add chicken. And then more spice (black pepper, lots) in the flour mix, if it needs it.
Can add flavour to the brine too of course- just boil the liquid, and infuse whatever you like in there.
Can do either, or both. If you want to use the buttermilk as a marinade, bring some up to 60/70 degrees, and add something to infuse (chilli, ginger, lemongrass, shallot?), then cool fully, put into the rest of the buttermilk, and add chicken. And then more spice (black pepper, lots) in the flour mix, if it needs it.
Can add flavour to the brine too of course- just boil the liquid, and infuse whatever you like in there.