Preheat the oven to 375°F (190°C). Make sure your 10-inch tube pan is completely clean and dry – any grease will prevent the cake from rising properly.

In a large, clean mixing bowl, combine the egg whites, cream of tartar, and salt. Beat on medium speed until foamy.

Gradually add ½ cup of the sugar, about 2 tablespoons at a time, while continuing to beat. Increase speed to medium-high and beat until medium-stiff peaks form – the egg whites should be glossy and hold their shape, but the tips will curl over when the beaters are lifted.

In a separate bowl, sift together the cake flour and remaining ½ cup sugar three times to ensure they're well combined and aerated.

Gently fold the flour mixture into the egg whites about ¼ cup at a time using a rubber spatula. Use a light hand with a cutting and folding motion to maintain as much volume as possible.

Add the vanilla extract and almond extract (if using) during the final few folds.

Carefully spoon the batter into the ungreased tube pan. Run a knife through the batter to eliminate any large air pockets.

Bake for 35-40 minutes, or until the top is golden brown and springs back when lightly touched.

Immediately invert the pan over a bottle neck or onto a cooling rack if your pan has feet. Allow the cake to cool completely upside down, about 1 hour.

Once cooled, run a thin knife around the sides and center tube to loosen the cake. Gently remove it from the pan.