You can find mixes for this in the store, but they cannot compare to scratch, and hot, dry weather is the perfect time to make it.
Preheat oven to 350. Separate a dozen eggs while cold, using caution to ensure no yolks make it into the whites. Bring whites to room temperature and stir in a tablespoon of water. Sift a cup of cake flour with a half cup sugar until it’s very light. (Yes, you can use plain flour.) You want to sift several times; some recipes say as many as five.
Beat the egg whites in a large, very clean, dry bowl. Start on a low speed. When the eggs are foamy, sprinkle in a teaspoon of cream of tartar. This acid helps stabilize the egg whites when they are whipped. Since most of the volume and structure of the cake comes from these egg whites, you’re not going to want to take the risk of substituting this ingredient. As the texture of the bubbles begins to even out, add a teaspoon or two of pure vanilla extract, and incorporate another cup of sugar bit by bit, about a tablespoon at a time.
Keep beating at a medium speed until the sugar is dissolved and the whites form stiff peaks. Then carefully FOLD in the flour while sifting it over the egg whites. Use a spatula, and turn the bowl; the key is not to deflate the bubbles. Make sure the flour is evenly combined throughout the whites, but don’t over-mix.
Gently pour the batter into a 10-in. ungreased tube pan; the cake has to cling to the sides as it rises, forming a bit of a crust. Bake for at least 30 minutes, until the top is crusty and springy.
Remove from oven and cool over a rack. You’ll find specially-made tube pans with legs for this cake. When cool remove by running a thin knife around the sides of the pan. You can buy a comb to slice this cake, otherwise use a serrated knife dipped in warm water.