Preheat a waffle maker according to the manufacturer’s instructions.
Place the egg yolks, milk, sour cream, butter and lemon juice in a large bowl. Whisk until well combined. Sprinkle the brown rice flour, millet flour, potato starch, flax meal, sugar, baking powder, baking soda and guar gum over the egg yolk mixture. Whisk until smooth.
Place the egg whites and salt in another large bowl. With an electric mixer on high speed, whisk the egg whites until stiff peaks form, about 2 minutes. Using a rubber spatula, fold a scoop of the egg whites into the batter; then carefully fold in the remaining egg whites with a rubber spatula.