Lemon Angel Food Cake

This cake started off as an innocent attempt to use up a cup+ of egg whites that were left over from some quiches I made last week. It ended as a pile of crumbs after we literally inhaled this cake before and after dinner last night.  But really, this is a nibbling cake, one that you can pull the spongy edges off of to get your sugar fix during the day. It's also a snack cake because it's light and airy and won't ruin your dinner (Yes, I am admitting that I ate cake before dinner and still had room for more cake after dinner.)
I had never made angel food cake before and feared a dry and crumbly cake- not based on anything rational, but just a general skepticism of any dessert that doesn't use much flour and absolutely no fat. But rest assured, the egg whites whipped up quickly and after only a few minutes, I had smooth shiny clouds of egg whites filling up my mixing bowl that not only looked like, but tasted like, heaven. And after about 35 minutes in the oven, out came a fluffy and spongy cake. It did a shrink a little - at least 2 inches down- and I'm not sure why. Ina's cake appears to be tall in her picture, certainly taller than mine was. But cut it up into slices, top it with some strawberries, and I guarantee you'll be left with just crumbs before anyone even notices.

Lemon Angel Food Cake
Adapted from Ina Garten

If you don't have cake flour in your pantry, you can make the following substitution: for every cup of flour, remove 2 tablespoons of flour, then add 1 tablespoon of cornstarch. So for this cake, follow this substitution, then add the additional 1/3 cup flour and proceed with the recipe.

2 cups sifted superfine sugar, divided
1 1/3 cups sifted cake flour (not self-rising) or use the substitution above
1 1/2 cups egg whites, at room temperature- 10 to 12 eggs. (I used 11 egg whites from standard large eggs)
3/4 teaspoon kosher salt
1 1/2 teaspoons cream of tartar
3/4 teaspoon pure vanilla extract
1 1/2 teaspoons grated lemon zest (approximately the zest of 2 lemons)

Preheat the oven to 350 degrees F. Combine 1/2 cup of sugar with the flour and sift together 4 times. Set aside. Place the egg whites, salt, and cream of tartar in the bowl of an electric mixer fitted with a whisk attachment and beat on high speed until the eggs make medium-firm peaks, about 1 minute. With the mixer on medium speed, add the remaining 1 1/2 cups of sugar by sprinkling it over the beaten egg whites. Whisk for a few minutes until thick and shiny. Whisk in the vanilla and lemon zest and continue to whisk until very thick, about 1 more minute. Sift about 1/4 of the flour mixture over the egg whites and fold it into the batter with a rubber spatula. Continue adding the flour by fourths by sifting and folding until it's all incorporated.

Pour the batter into a greased 10-inch tube pan, smooth the top, and bake it for 35 to 40 minutes, until it springs back to the touch. Remove the cake from the oven and invert the pan on a cooling rack until cool. Cut into slices and serve with strawberries if desired.