01 - Preheat oven to 300°F and line a baking sheet with parchment paper.
02 - In a large, clean mixing bowl, beat separated egg whites with cream of tartar until soft peaks form. Gradually incorporate sugar while continuing to beat until stiff, glossy peaks develop.
03 - In a separate bowl, whisk together egg yolks, cornstarch, and vanilla extract until the mixture is smooth and even.
04 - Gently fold the egg yolk mixture into the whipped egg whites, being careful not to deflate the airy batter.
05 - Divide the batter evenly among several bowls based on the number of colors desired. Add a few drops of gel food coloring to each portion and fold gently to achieve vibrant hues.
06 - Spoon colorful batter portions onto the prepared baking sheet, placing them side by side for a rainbow effect. Swirl the colors gently with a spatula for a marbled pattern.
07 - Transfer baking sheet to oven and bake for 25 minutes, or until set and lightly golden.
08 - Allow cloud bread to cool for several minutes before removing from baking sheet. Serve immediately to enjoy optimal fluffiness.