01 - Preheat oven to 300°F. Line a baking sheet with parchment paper.
02 - In a large, clean mixing bowl, beat the egg whites and cream of tartar until soft peaks form. Gradually add sugar, beating continuously until stiff, glossy peaks are achieved.
03 - In a separate bowl, whisk together the egg yolks, cornstarch, and vanilla extract until the mixture is smooth and well-combined.
04 - Gently fold the egg yolk mixture into the whipped egg whites, taking care not to deflate the batter.
05 - Divide the batter evenly into separate bowls based on the number of colors desired. Add a few drops of gel food coloring to each bowl and gently fold to fully incorporate.
06 - Using a spoon, place colorful dollops side by side onto the prepared baking sheet to create a rainbow pattern. Swirl gently with a spatula if marbled effect is preferred.
07 - Bake in the oven for 25 minutes, or until the bread is set and lightly golden.
08 - Remove from the oven and allow to cool briefly before lifting from the baking sheet. Serve immediately for optimal fluffiness.