For the starter: In a medium bowl, mix together the flours and sugar., Stir in the buttermilk and starter. Cover with plastic wrap and let sit at room temperature overnight., For the batter: Beat together the eggs, butter (or oil), salt, and baking soda. Stir into the starter; it will immediately start to form bubbles., Place a rack on a baking sheet, put it in the oven, and preheat it to 200°F., To cook: Preheat a waffle iron, grease when hot, and cook according to the manufacturer's instructions, until the waffle is golden brown., 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.