1. Preheat oven to 375 degrees F. Have an ungreased 9×13 cake pan ready.
2. Sift half of the sugar with the flour and salt. Repeat 5 times. Set aside.
3. Whip egg whites with a mixer on low speed until frothy, then add vanilla extract and cream of tartar.
4. Increase speed to medium and continue whipping, adding remaining sugar 1 tablespoon at a time.
5. Increase to medium-high and whisk until stiff, glossy peaks, scraping sides and bottom of bowl once if needed.
6. Sift about 1/4 cup of the flour mixture on top of the whipped egg whites and fold gently to incorporate. Repeat until all flour the flour has been added.
7. Add the batter to the cake pan, smooth the top, then run a knife through batter to break any air bubbles.
8. Bake until lightly golden on top and a toothpick inserted in the middle comes out clean, about 15-20 minutes.
9. Cool upside down for about an 1 hour. I used 4 cans that are the same height and put one can under each corner of the pan.
10. 
Once cooled, run a thin knife or offset spatula between the cake and the sides of the cake pan to loosen it.
11. To make the whipped cream, add the heavy whipping cream, powdered sugar and vanilla extract to a large mixer bowl. Whip on high speed until stiff peaks form.
12. Set aside about 1 1/2 cups of whipped cream and spread the rest into an even layer on top of the angel food cake.
13. Used the sliced strawberries and blueberries to create the flag design.
14. Use the remaining whipped cream to pipe “stripes” between the strawberry rows. I used Ateco piping tip 844, but you could also use Wilton 1M or 2D
15. Refrigerate cake until ready to serve. Cake is best when served the day it’s made because of the fresh fruit on top. If you want to make it ahead a day ahead, I’d suggest adding the fruit and whipped cream “stripes” shortly before serving.