Preheat oven to 325°F (160°C) with rack in lower third. Sift together flour, cocoa, and half the sugar (3/4 cup) twice.

Beat egg whites with cream of tartar and salt on medium until foamy, then on high, gradually add remaining 3/4 cup sugar and beat to stiff, glossy peaks. Beat in vanilla and almond extract if using.

Fold dry mixture into whites in three additions with a rubber spatula, gently mixing just until no streaks remain.

Spoon batter into an ungreased 10-inch tube pan. Smooth top and run a knife through to remove air bubbles.

Bake 40 to 45 minutes until golden and top springs back. Invert pan immediately and cool completely, about 2 hours.

Loosen edges with a thin knife, remove from pan, and slice with a serrated knife to serve.