1. Preheat oven to 350 degrees. Sift flour, cocoa powder, and salt into a small bowl.

2. Whisk whites with a mixer on medium-high speed until soft peaks form. Gradually add 2/3 cup sugar, whisking until stiff, shiny peaks form, about 5 minutes. Whisk yolks with remaining 2 tablespoons sugar in a medium bowl until thick and pale, about 3 minutes. Fold yolk mixture into whites, then fold in flour mixture in 2 additions.

3. Line 2 baking sheets with parchment. On 1 piece, draw two 6-inch circles, then flip parchment over. Spoon batter into a pastry bag fitted with a 1/2-inch round tip. Starting in the center of each circle, pipe a spiral, leaving a 1-inch border around inside edge of circle. Bake until springy to the touch, 15 to 18 minutes. Transfer parchment with rounds to a wire rack, and let cool.

4. On the other piece of parchment, draw 4 rows, each 3 1/2 inches wide for the ladyfingers. Pipe 1-inch-wide ladyfingers horizontally between pairs of lines, so they're touching, and lightly dust with cocoa. Bake until springy to the touch, about 15 minutes. Transfer parchment with ladyfingers to a wire rack, and let cool. Use immediately.