Preheat the oven to 375 degrees, with a rack in the center.
FOR THE CAKE: Mix the sugar and water in a saucepan, bring to a boil, and cook over medium heat for 2 minutes to make a light syrup. Put the egg yolks in the bowl of a mixer or another large bowl. Slowly pour the hot sugar syrup over the yolks, mixing vigorously with the whisk. Continue whipping the mixture for about 5 minutes, until fluffy, smooth, and pale yellow in color. Add the melted chocolate and coffee and mix well.
Whip the egg whites in a large bowl until they hold firm peaks. Add about one third of the whites to the chocolate mixture and mix vigorously with the whisk. Add the remaining whites and fold in with a rubber spatula, mixing just enough to combine the ingredients; do not overmix.
Cut a piece of parchment paper large enough to line a 12- by 16-inch baking sheet (or use a nonstick baking mat). Butter the paper and coat with flour, shaking off any excess.
Spread the batter in the pan; it will be about 1/2 inch thick. Bake for about 12 minutes until set and puffy. Cool to room temperature; then cover with plastic wrap. (Rolling the cake is a delicate operation, but the wax paper aids in the removal and rolling of the cake. The plastic wrap keeps the cake moist, making it possible to be rolled.)
FOR THE FILLING: Whip the cream until it holds a soft peak. Add the confectioners’ sugar, vanilla, and kirsch and continue beating until the cream is firm.
TO ROLL THE CAKE: Remove the plastic wrap and slide a knife all around the sides to loosen the cake. Spread the whipped cream on the cake. Starting from a long side, roll up the cake, with the wax paper still on, peeling the paper off a little at a time as you roll the cake; avoid pressing down on the cake as you roll, so that the whipped cream is not squeezed out. Continue rolling and removing the paper, and finish with the seam underneath so that the cake looks smooth on top. Use two large spatulas to slide the cake onto a serving platter. Put the cocoa powder in a sieve and shake it over the cake to coat the top. Refrigerate until ready to serve.
Cut into slices and serve.
Copyright © 2011 by Jacques Pépin. Used by permission of Houghton Mifflin Harcourt. All rights reserved.
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