Place separated egg whites into a mixing bowl along with the cream of tartar and set aside. Place egg yolks in another bowl and add remaining ingredients one by one, making sure to stir after each addition. Whip eggs whites and cream of tartar until still, then fold into egg yolk mixture. Pour mixture evenly into nonstick, buttered muffin pans and bake at 350 degrees for 30 – 35 minutes.