01 - Preheat oven to 300°F. Line a baking sheet with parchment paper.
02 - In a clean, dry mixing bowl, beat egg whites and cream of tartar using an electric mixer until soft peaks form. Gradually add sugar, continuing to beat until stiff, glossy peaks are achieved.
03 - In a separate bowl, whisk together egg yolks, cornstarch, and vanilla extract until a smooth texture is obtained.
04 - Gently fold the egg yolk blend into the whipped egg whites, taking care to retain volume.
05 - Divide batter evenly among bowls for each desired color. Add a few drops of gel food coloring to each portion and fold gently until colors are well incorporated.
06 - Spoon colored batters onto prepared baking sheet side by side to create a rainbow effect. Optionally, lightly swirl with a spatula for a marbled appearance.
07 - Bake for 25 minutes, or until set and lightly golden.
08 - Allow cloud bread to cool briefly before removing from baking sheet. Serve immediately to enjoy maximal fluffiness.