Preheat oven to 350°F. Place the egg whites in the clean bowl of a stand mixer fitted with the whisk attachment. Begin whipping the egg whites on low speed. After about 2 minutes, a microfoam will begin to form. Once a microfoam has formed, sprinkle in the cream of tartar and salt and continue whipping on low. After about 1½ minutes, the egg whites will have slightly increased in volume and faint whisk lines will become visible in the egg white foam. While the mixer is running, slowly stream in the sugar, giving it time to dissolve.
12 egg whites, 1½ teaspoons kosher salt, ¾ teaspoon cream of tartar, 1⅛ cups granulated sugar
Once the sugar is completely incorporated, increase the mixer speed to high and whisk to stiff peaks. This will take anywhere from 12-20 minutes depending on the humidity. Do not increase speed higher than 4. This constant, slow speed creates a steady, stiff meringue that will not fall. Do not rush this part. Whipping your meringue at a higher speed will still give you a stiff meringue but it will not be as dense and will have the tendency to fall or get way too soft when adding the flour mixture.
While the meringue is whipping: In a medium-sized bowl, sift the cake flour, powdered sugar, and cocoa together. Sifting them together aerates the mixture which will help in the even texture of the cake. If there are any large chunks of powdered sugar left in the sieve, discard them. Set aside until the meringue is done.
¾ cups cake flour, ½ cup unsweetened cocoa powder, 1¼ cups powdered sugar
After about 12-13 minutes of whipping, the egg whites you should have soft peaks. With the mixer still going, add in the vanilla extract. Continue whipping the egg whites for about 8 more minutes, or until very stiff peaks have formed. After 18 minutes of the meringue whipping, stop and check it about every 45 seconds by pushing the whisk through and pulling up. If when you pull the whisk out of the meringue and your peak falls over slightly, it is not stiff enough. A good meringue will have stiff peaks as well as some noticeable resistance when the whisk is pushed through it. Once you have reached stiff peaks, do not keep whipping, as the meringue can be overwhipped and get soft and can no longer be whipped back stiff. If that happens, start over. Do not let your meringue sit for more than a couple of minutes before adding in your flour mixture as it will start to deflate.
1 teaspoon pure vanilla extract
Add in the flour, powdered sugar, and cocoa mixture to the meringue. Using a rubber spatula, gently fold them together until they are homogeneous. Using a rubber spatula is ideal as it scrapes the sides of the bowl well. Be sure that you scrape the bottom of the bowl as well as the sides, as flour tends to set down there and not get incorporated. Take care not to deflate the meringue.
Carefully pour the batter into an ungreased angel food cake tube pan and spread evenly throughout. It is important that you do not grease this pan as any oil will deflate the meringue. The cake will cling to the sides and rise as it is supposed to.
Place into the preheated oven and bake for 35-40 minutes or the cake begins to pull away from the sides and it springs back when touched. Once baked, remove from the oven and place upside down onto a cooling rack, plate or cake stand. Allow to cool for about 1 hour. Carefully run a butter knife around the edges of the pan on both the outside edge and the inside tube. Remove the cake from the pan.
Pipe on or cover your cake with chocolate whipped cream and strawberries for extra garnish. Serve and enjoy!
Chocolate Whipped Cream Frosting