Preheat your oven to 350°F (175°C) and position the oven racks in the center.

In a large bowl, whisk together the gluten-free flour blend and cornstarch until well combined.

Blend white sugar in a food processor until super-fine.

In a clean bowl, combine egg whites, cream of tartar, and salt. Beat until frothy, then increase speed and whip until soft peaks form.

Gradually add the processed super-fine sugar while beating until glossy and medium-stiff peaks form.

Fold the flour mixture into the egg whites in three separate additions.

Pour the batter into an ungreased nonstick angel food cake pan and smooth the top.

Bake for 45-47 minutes until golden brown and springy to the touch.

Cool the cake upside down on a cooling rack for at least one hour.

Run a serrated knife around the sides, release the cake, and slice to serve.