Preheat oven to 300°F.Whisk egg whites until they become frothy by hand or in the bowl of a stand mixer. Once bubbly, add sugar and cornstarch. Add food coloring and vanilla extract if using. Whisk mixture until glossy, thick, and forming stiff peaks.Scoop the mixture out onto a baking sheet lined with parchment paper. Form into a round, “cloud-like” shape.Bake for 20 to 25 minutes.