Preheat oven to 325ºF. Sift flour with 1/3 cup sugar 3 times; set aside.
In large bowl, whip egg whites and salt with electric mixer until foamy; add cream of tartar and beat until soft peaks form. Gradually beat in 2/3 cup sugar, whipping until soft peaks form and mixture is glossy. Beat in vanilla.
Fold in flour mixture and sprinkles until completely incorporated. Divide batter evenly among pans, filling about 3/4 full. Run a knife through the batter and tap pans gently against the counter to settle batter; smooth tops. Place pans on a baking sheet and bake 40-45 minutes until top is browned and cake tester comes out clean. Invert pans on cooling grid and cool cakes completely.
Loosen sides of cakes from pan with spatula; remove from pans. Serve with whipped cream, if desired.