How to Make It
Preheat oven to 375°.
To prepare cake, weigh or lightly spoon white rice flour, cornstarch, sweet white sorghum flour, and almond meal flour into dry measuring cups; level with a knife. Combine white rice flour, cornstarch, sweet white sorghum flour, almond meal flour, 3/4 cup granulated sugar, cocoa, and xanthan gum in a medium bowl; stir with a whisk.
Place egg whites in a large bowl; beat with a mixer at high speed until foamy. Add cream of tartar and salt; beat until soft peaks form. Gradually add 3/4 cup granulated sugar, 2 tablespoons at a time, beating until stiff peaks form. Add almond extract; beat well. Sift flour mixture over egg white mixture, 1/4 cup at a time; fold in.
Spoon batter into an ungreased 10-inch tube pan. Break air pockets by cutting through batter with a knife. Bake at 375° for 45 minutes or until cake springs back when lightly touched and small cracks form on top of cake. Invert pan (but don’t remove from pan); cool completely. Loosen cake from sides of pan using a narrow metal spatula. Invert cake onto a plate.
To prepare glaze, combine powdered sugar and remaining ingredients in a small bowl; stir with a whisk until smooth. Spoon over cake. Let stand 10 minutes or until glaze is set. Cut cake into 12 slices.
If your angel food cake pan doesn't have feet to set on for cooling, invert the pan on the neck of a wine bottle.