Preheat oven to 300 degrees F. Line a pan with parchment paper or a Silpat mat.
Mix egg whites & cream of tartar on high speed until stiff peaks form.
In a large bowl mix egg yolks & greek yogurt (or cream cheese) until well combined and smooth. Gently fold in about 1 cup of the egg white mixture until well combined. Add remaining egg whites and fold just until mixed.
Divide egg mixture into 6 equal portions on prepared pan. Spread until about 1/2″ thick.
Bake 30 minutes or until lightly browned. Immediately move to a wire rack and cool completely (at least 60 minutes).