Preparation / Directions:
* Note: If you have a fraction more or less than 2 cups, it doesn't matter. Preheat oven to 375 degrees. Adjust oven rack so it is 1/3 of the way up from the bottom. To measure the cake flour: Dip a 1-cup measure into the cake flour container, scoop up the flour, and sweep off the excess with a knife. Combine the measured flour with half the sugar (3/4 cup) in a small bowl, stirring them together with a for or wire whisk. Sift them together 3 times. Place the remaining sugar (3/4 cup) in a small cup. A standing electric mixer is the easiest way to make an angel food cake. Put the egg whites in the largest bowl. Turn to the LOWEST speed. After about a minute, when the whites are broken up, and resemble a foamy syrup, stop beating, and add the cream of tartar, vanilla and salt. Take about 30 seconds to gradually turn to MEDIUM speed, then, holding the reserved 3/4 cup sugar at the edge of the bowl, gradually let sprinkles of it drift into the whites. Stop beating when all the sugar is added, and scrape around the sides and bottom of the bowl with a rubber spatula. Resume beating at MEDIUM speed until the whires are "stiff but moist". The next step is folding in the light, beaten egg whites with the heavier flour mixture, without deflating the egg whites. The easiest method, and it's almost foolproof: Sift about1/3 of the flour/sugar mixture over the top of the egg whites, and using the same beaters, turn the machine to the LOWEST speed for a few seconds...until blended, and there are no drifts of flour visible. Stop and scrape all around the bowl with a rubber spatula. Sift on half the remaining flour mixture, and beat at the LOWEST speed, until just blended, then scrape all around again. Fold in the last of the mixture the same way.
FILLING THE CAKE PAN: The batter will lose volume if it stands around. Fill the 10" ungreased tube pan immediately. Hold the bowl over the pan as you pour, so the batter is even. Scrape out the bowl with a rubber spatula or your hand. With a long knife, cut through the batter several times, to pop any air bubbles. Smooth the top with a rubber spatula. Place the cake in the preheated oven, on the middle rack.
Bake for 40 to 45 minutes. The cake will probably rise to the top of the pan, or a little above it. Make the first test for doneness after 30 minutes: insert a long broom straw or thin wooden skewer into the middle of the cake. If it comes out clean, the cake is done. The cake will be lightly browned, and will spring back when you press it gently with your finger. Remove the cake from the oven, and immediately invert the pan. Let the cake cool upside down until the pan no longer feels warm. (Overnight is okay.) Remove the cake, and fr