Preheat Oven. Adjust oven rack to the middle position and remove the top rack. Preheat oven to 350°F (180°C). Sift gluten-free flour and set aside.(This removes any lumps in the gluten-free flour.)

Whip the Egg Whites. Stir together granulated sugar, cream of tartar, and salt in the bowl of a stand mixer fitted with the whisk attachment. Add egg whites and vanilla extract. Whisk on low to combine, about 1 minute. Increase speed to medium-high (6-8 on a KitchenAid) and whip 6 minutes.

Increase speed to high (10 on a KitchenAid) and whip until the meringue is shiny, white, and thick. This takes between 2-4 minutes. The tines of the whisk should leave a pattern in the meringue. Stop the mixer and remove the whisk attachment from the bowl. The meringue clinging to the whisk should form a very soft peak. You want it to fall in a thick ribbon off the whisk. Replace the whisk and turn the mixer back on to high speed.

Slowly the Gluten-Free Flour. Add the flour, 1/4 cup at a time, and mix until incorporated. Allow each addition of flour to incorporate before adding the next.

Bake the Cake. Spoon batter into an ungreased 10-inch aluminum tube pan. Bake until the cake is golden brown and firm to the touch, about 50 minutes. (The internal temperature of the cake should be 206°F.)

Cool the Cake. Remove pan from the oven and immediately invert onto the legs of the pan. If the pan does not have legs, invert onto the neck of a wine bottle. Cool for at least 2 hours. If the kitchen is cold, place the pan on top of the oven to cool and prop the oven door open. 

Remove the Cake from the Pan. Slide an offset spatula around the sides of the cake to loosen. Remove the insert, and slide a spatula under the bottom of the cake. Gently lift the cake off the insert and place onto a serving dish.

To serve, cut with a serrated knife. Store leftovers wrapped tightly in plastic for up to 1 week at room temperature.