Meanwhile, add cream of tartar to the egg whites and on high speed, whip whites until form stiff peaks (no longer slide when tilt the bowl) – DON’T over whip. While whites are whipping, add salt to egg yolks. Using a hand mixer, mix yolks on high speed until very well mixed. Slowly pour yolks over whites. Using a spatula, gently fold yolks into whites together until well blended.