Start by preheating your oven to 350°F (175C/155C Fan).
Place your egg whites, cream or tartar and vanilla extract into a large mixing bowl and begin beating with a handheld electric beater until soft peaks form.
9 egg whites, 1¼ teaspoon cream of tartar, 1 teaspoon vanilla extract
While continuing to beat, slowly add 1 cup of your sugar (about a tablespoon at a time). Once you've finished adding the sugar, beat on a high speed until glossy and thick stiff peaks form.
1½ cups granulated sugar
Set the meringue aside and in a separate mixing bowl sift together your flour, remaining ½ cup sugar, cornstarch, salt and blueberry powder. Sift this twice.
¾ cup all purpose flour, 2 tablespoon cornstarch, ¼ teaspoon salt, 1 tablespoon freeze dried blueberry powder, 1½ cups granulated sugar
Add the dry ingredients to the meringue mixture and fold to combine. Avoid over-beating and knocking too much air out of the meringue, but ensure that there are no unmixed pockets of dry ingredients.
Pour the mixture into your Angel Food pan - this is often best done with a large spoon to ensure you get an even coverage around the central hole.
Sprinkle your fresh blueberries over the top.
6 oz fresh blueberries
Using a kitchen knife, swirl through the batter - this will help to remove air bubbles but will also help to mix the blueberries into the cake.
Place the cake in the preheated oven and bake for about 40 minutes until risen and the top has gone golden. It should appear dry and a bit crackly on top.
Once baked, remove from the oven and immediately invert over a plate or piece of parchment paper. Allow the cake to cool upside down - this will help the cake to preserve it's lightness and the meringue's rise.
After cooling for at least an hour, use a kitchen knife to carefully scrape around the sides and base of the pan, releasing the cake. (see note)