Place the egg whites in the bowl of your mixer so that they will warm to room temperature. Egg whites at room temperature yield more volume and whip easier than cold egg whites.Place the egg yolks in a Tupperware container with a cover. Store the yolks in the refrigerator to add to your scrambled eggs the next morning. (My mother always said that there’s nothing like a little extra protein for breakfast to give you a head start to the day. I once tried to convince her that cookies had extra protein, but it didn’t work.)Hannah’s 1st Note: I always use a stand mixer when I make these cookies. It’s a lot easier than whisking egg whites by hand in a copper bowl.Prepare your baking sheets by lining them with parchment paper (works best) or brown parcel-wrapping paper (also works, but parchment is preferable). Spray the paper with Pam or another non-stick cooking spray and dust it lightly with flour. You can also use baking spray, which is cooking spray mixed with flour.Beat the egg whites with the cream of tartar, vanilla, and salt until they are stiff enough to hold a soft peak.