Preheat the oven to 140°C/275°F/gas mark 1 and place a baking sheet in the oven. Sift together the flours, baking powder, spices and salt and set aside.
Place the mashed sweet potato in a large bowl and whisk in the oil and brown sugar followed by the milk and egg yolks. Stir in the dry ingredients.
Place the egg whites in a large, spotlessly clean bowl and whisk with an electric mixer until they just form stiff peaks.
Gently fold the egg whites into the batter, being careful not to knock out too much of the air.
Recipe adapted from: http://www.geniuskitchen.com/recipe/sweet-potato-waffles-117479?ftab=reviews