Special equipment: a 9-inch angel food cake pan
Preheat the oven to 375 degrees F.
For the cake: Sift the cake flour with the cocoa and 3/4 cup of the sugar into a large bowl.
Using an electric mixer fitted with the whisk attachment, beat the egg whites with a pinch of salt until foamy. Sprinkle the cream of tartar over the egg whites and continue to beat until they hold a soft peak. Add the vanilla extract and gradually beat in the remaining 3/4 cup sugar, about 2 tablespoons at a time.
Remove the bowl from the mixer and, using a spatula, gradually fold in the flour mixture, sprinkling in about 1/4 cup at a time. Pour the batter into an ungreased 9-inch angel food cake pan and bake until the cake springs back when pressed with your finger, about 30 minutes. Let cool for 1 hour, then loosen the cake from the sides and center of the pan with a knife before unmolding.
For the strawberries: Combine the strawberries and sugar in a medium bowl and toss gently to coat every slice. Let the strawberries stand for about 30 minutes to allow the juices to develop. Serve over the chocolate angel food cake.
Adapted from "Trisha's Table: My Feel-Good Favorites for a Balanced Life" by Trisha Yearwood (c) Clarkson Potter 2015. Provided courtesy of Trisha Yearwood. All rights reserved.