Sift together half of the sugar with the flour or cornstarch (if using), and set aside.
In a clean, dry mixing bowl, whip the egg whites using an electric mixer on medium speed until foamy.
Add the cream of tartar and continue whisking until soft peaks form, which means the whites hold a slight bend when you lift the beaters.
Gradually add the remaining sugar, a few tablespoons at a time, while whisking at high speed. Continue until stiff, glossy peaks form that stand up straight when you lift the beaters.
Gently fold in the vanilla extract using a spatula.
Carefully sift in the dry mixture over the whipped egg whites, a little at a time, folding gently after each addition. Be careful not to deflate the fluffy mixture.
Pour the batter into an ungreased tube pan. Smooth the top gently with a spatula or the back of a spoon.
Bake in a preheated oven at 350°F (175°C) for about 35 minutes, or until the cake is golden brown and a toothpick inserted into the center comes out clean.
Remove the cake from the oven and immediately invert the pan onto a bottle or cooling rack to cool completely upside down, which helps keep it airy and prevents collapsing.
Once cooled completely, run a thin knife around the edges of the pan to loosen the cake, then carefully lift it out.
Slice gently with a serrated knife and serve alone or with fresh berries. The cake should be light, fluffy, and tender with a slightly crisp crust.
