In a large bowl, add the egg whites. Let them sit at room temperature for 30 minutes. Sift the powdered sugar and flour together twice; set aside.
To the egg whites in the bowl, add the cream of tartar, extracts and salt. Use an electric mixer to beat this mixture on medium speed until soft peaks form. Gradually add the sugar (about 2 tablespoons at a time), beating on high until stiff glossy peaks form and the sugar is dissolved. Gradually fold in the flour mixture, about ½ cup at a time.
Gently spoon the batter into an ungreased 10-inch tube pan. Cut through the batter with a knife to remove air pockets. Bake on the lowest rack at 350°F for 40 to 45 minutes (or until lightly browned and the entire top appears dry). Immediately invert the pan; cool completely, about 1 hour.
Run a knife around the side and the center of the tube pan. Remove the cake to a serving plate. Slice and eat plain, or top with whipped cream and berries!