01 - Preheat oven to 300°F (150°C). Line a baking sheet with parchment paper.
02 - In a large, clean bowl, beat egg whites and cream of tartar until soft peaks form. Gradually add sugar, beating until stiff, glossy peaks are achieved.
03 - In a separate bowl, whisk egg yolks, cornstarch, and vanilla extract until smooth.
04 - Gently fold the yolk mixture into the whipped egg whites, keeping the batter airy.
05 - Divide the mixture evenly among separate bowls for each color desired. Add a few drops of gel food coloring to each portion and gently fold until color is uniform.
06 - Spoon colored batters side by side on the prepared baking sheet to create a rainbow effect, swirling gently with a spatula for a marbled appearance if preferred.
07 - Bake at 300°F (150°C) for 25 minutes, until set and lightly golden.
08 - Allow to cool for several minutes before removing from the baking sheet. Serve immediately for optimal fluffiness.