For the Angel Food Cake:

• Preheat oven to 325º, with rack in the lower third of the oven.
• Place egg whites in a large mixing bowl. Beat on medium speed until frothy, about 1 minute. Add the cream of tartar, lemon juice, vanilla, and salt; continue beating until soft peaks form, about 2 1/2 minutes. With mixer running, add remaining cup sugar a little at a time, beating no longer than 1 minute.
• Raise speed to medium-high; continue beating until firm, but not stiff, peaks form (when beater is lifted, only the tip of the peak should fall over slightly). Gently transfer egg-white mixture to a large, wide bowl. Sprinkle a third of the reserved flour mixture over the whites. Using a whisk, gently combine in a folding motion, allowing batter to fall through the whisk as you fold. Sprinkle the remaining flour mixture over whites in two more batches; fold until just combined. Be careful not to overmix because the egg whites will deflate.
• Using a large rubber spatula, transfer batter to prepared pan. Run a knife gently through the center of the batter to remove any large air bubbles. Bake until a cake tester inserted in the middle comes out clean and cake is springy to the touch, 45 to 50 minutes.
• Remove pan from oven and invert onto its legs, making sure cake clears the surface of the counter. Let cool completely, 1 1/2 to 2 hours. To remove cake, reinvert pan, top side up. Run a knife around the inner and outer edges of the cake before releasing the bottom. Cake will keep up to 2 days at room temperature in an airtight container or wrapped in plastic. To serve, slice with a serrated knife.

For the Cocoa Whipped Cream and Almonds: