01 - Preheat oven to 300°F. Line a baking sheet with parchment paper.
02 - In a clean mixing bowl, beat egg whites with cream of tartar until soft peaks form. Gradually add sugar, continuing to beat until stiff, glossy peaks are achieved.
03 - In a separate bowl, whisk egg yolks, cornstarch, and vanilla extract until smooth.
04 - Gently fold the egg yolk mixture into the whipped egg whites, maintaining the aerated texture.
05 - Divide batter evenly into separate bowls for each color. Add a few drops of gel food coloring to each bowl and gently fold to incorporate.
06 - Spoon colored batters side by side onto the prepared baking sheet to form a rainbow effect. Swirl with spatula if marbling is desired.
07 - Bake for 25 minutes, until set and lightly golden.
08 - Allow to cool briefly. Lift from parchment and serve for maximum fluffiness.