Preheat oven to 350°F. Add egg whites, salt, and cream of tartar to the bowl of as and mixer.
Whip on high speed until foamy and light. Then, gradually add half the sugar (3/4 cup) and continue whipping.
Whip egg whites until stiff peaks. They should stand up with no resistance. Remove bowl from stand mixer.
In a separate bowl, measure flour, the rest of the sugar (3/4 cup), 1 cup toasted coconut, and cornstarch.
Gradually and softly fold the dry ingredients into the egg whites with a spatula. Continue until no streaks remain.
Transfer cake batter to an angel food cake pan and smooth evenly. Cook for 35 - 45 minutes until risen and golden brown on top.
Remove from oven and rest pan upside down for at least 2 hours. Then carefully remove from pan by running a knife around the edges.
Slice angel food cake into equal portions and top with whipped cream and extra toasted coconut.