Preheat your oven to 325 degrees Fahrenheit.
Measure the all purpose flour and cornstarch (or the cake flour, if using) and 1 1/2 cup powdered sugar very carefully into a large bowl. Whisk together with a wire whisk.
Sift the flour mixture into another large bowl using a fine sieve or flour sifter. Sift the flour mixture back into the first bowl and then again into the second bowl (so you'll sift the mixture at least 3 times). Set aside.
Add the egg whites to a large mixing bowl or to the bowl of your stand mixer fitted with the whisk attachment.
Whip on medium speed until foamy. Add the cream of tartar and salt.
Continue whipping on high speed until soft peaks form.
While continuing to whip on medium-high speed, add the 3/4 cup powdered sugar slowly - about 2 tablespoons at a time - until it's fully incorporated.
Increase the speed to high and whip until hard peaks form, adding the vanilla as it whips.
Using a wire whisk, fold the flour mixture into the whipped egg whites about 1/4 cup at a time, making sure to fold very gently and slowly, so as not to deflate the egg whites. This is a critical step, so take care and take your time.
Pour the batter slowly into an un-greased 10-inch angel food cake or tube pan and smooth out the top carefully.
Bake for 35-40 minutes at 325 degrees Fahrenheit or until the top of the cake is golden brown and the cake springs back when you touch it gently.
Invert the cake to cool (turn it upside down) on a glass to promote air flow. Cooling the cake upside down with lots of airflow will ensure that it doesn't fall as it cools and that it maintains its grand height.
Let the cake cool completely to room temperature (I let it cool for at least an hour) before slicing and serving with fresh berries (or your favourite fruit sauce) and whipped cream.