Preheat oven to 300°F. Line a baking sheet with parchment paper.
Carefully separate your egg whites from the yolks, placing them in two separate bowls. Make sure no yolk gets into the whites—even a small amount of fat from the yolk can prevent the whites from whipping properly.
Add the cream of tartar to the egg whites and beat with an electric mixer on high speed until stiff peaks form. This typically takes 2-3 minutes.
In a blender or food processor, blend the cottage cheese until completely smooth with no visible curds. Add this to the bowl with your egg yolks along with the salt and sweetener (if using). Mix until well combined.
***This is the most important step for achieving that signature cloud bread texture*** Gently fold the yolk mixture into the whipped egg whites using a spatula. Use slow, sweeping motions from the bottom of the bowl to the top, rotating the bowl as you go. The goal is to incorporate the mixtures without deflating the egg whites.
Using a ¼ cup measuring cup, scoop the batter onto the prepared sheet, spacing the mounds about 2 inches apart—they will spread slightly during baking. Gently smooth the tops with the back of a spoon.
Bake at 300°F for 25 minutes, or until the tops are golden brown and the bread feels set when gently touched.
Allow the cloud bread to cool on the baking sheet for 5 minutes before transferring to a wire rack. The bread will be soft and slightly pliable when warm, then firm up slightly as it cools. Serve as a bread alternative with your favorite toppings or use for sandwiches.