How to Make It
Whisk together the sugar, ¼ cup salt, peppercorns, and 2 cups warm water until dissolved in a large bowl. Add the pork chops to the brine, cover, and refrigerate for at least 30 minutes and up to 12 hours.
Heat 2 tablespoons of the oil in large skillet over medium-high heat. Add the onion and ¼ teaspoon each salt and pepper. Cook, stirring occasionally, until brown, 8 to 10 minutes. Add the vinegar and toss to combine. Wipe out the skillet; reserve.
Drain the pork chops and pat dry. Heat the remaining tablespoon of oil in the reserved skillet over medium-high heat. Cook the chops, in batches, until an instant-read thermometer inserted into the thickest chop registers 145° F, 5 to 6 minutes per side, reducing the heat if the pan becomes too dark.
Meanwhile, steam the potatoes in ½ inch water until tender, 15 to 18 minutes, adding the kale during the last 2 minutes of cooking. Drain; return to pot. Add the butter, milk, and ½ teaspoon each salt and pepper and mash.
Serve the potatoes and pork chops warm slathered with the onions.