Preheat a waffle iron. Place a rack on a baking sheet, put it in the oven , and preheat it to 200°F., In a medium bowl, combine the potatoes, salt, egg yolks, and butter (or oil), mashing and mixing until the mixture is lump-free., Beat in the buttermilk., In a separate bowl, whisk together the flour, baking powder, baking soda, chives (or scallions), and the crumbled bacon., Add this mixture to the wet ingredients and mix until just combined., In a clean, grease-free bowl, beat the egg whites until stiff but not dry and fold them into the batter., Cook the waffles immediately according to the manufacturer's instructions; this batter will not hold well., Transfer the finished waffles to the oven to keep warm while you cook the remaining batter., Leftover waffles can be frozen for a few weeks, and reheated in the toaster.