For cake: 6 ounces quality bittersweet chocolate, chopped 3 Tablespoons water 6 large eggs, separated (room temperature) 2/3 cup sugar plus 2 Tablespoons 1/4 teaspoon salt 1 Tablespoon cocoa powder
For filling: 1 cup heavy cream 1/4 cup powdered sugar 2 Tablespoons Chambord
For topping: 2 Tablespoons cocoa powder 2 Tablespoons powdered sugar Mint leaves for garnish
Preheat oven to 350°F.
Butter a 15x10x1" baking dish. Line bottom with parchment paper allowing 2" excess parchment to hang over ends.
Melt chocolate and 3 tablespoons water in a double boiler set over simmering water; stirring occasionally until smooth and glossy. Remove from heat and let cool to room temperature.
Place egg yolks, 2/3 cup sugar, and salt in a large bowl (or in work-bowl of a stand mixer) and beat until pale and thick, about 5 minutes in a stand mixer and about 8 minutes with an electric hand-held mixer. Fold in melted chocolate until just blended.
In a separate bowl, (using clean beaters), beat egg whites until soft peaks form. Add remaining 2 tablespoons sugar and continue to beat until whites just hold stiff peaks.
Fold in one quarter of egg whites into chocolate mixture to lighten, then fold in remaining whites gently but thoroughly.
Spread batter evenly into prepared pan.
Bake in center of oven until puffed and dry to the touch, about 15-18 minutes.
Transfer pan to a rack and cover with 2 layers of dampened paper towels. Let stand for 5 minutes.
Remove paper towels and let cool completely. Loosen edges with a sharp knife.
Sift cocoa powder over top of cake.
Lay a large sheet of wax paper on top of cake (making sure it runs the full length of cake). Place a baking sheet over paper and invert cake onto it. Carefully remove parchment paper. (The cake may crack, but don’t worry it will still work.)
Beat cream with powdered sugar and Chambord until stiff peaks form.
Spread filling evenly over cake. Put a long platter next to the long side of cake. Using wax paper as an aid, roll up cake (lengthwise). Carefully slide cake, seam-side down, onto long platter. (Cake will crack - but it will still hold together.)
Dust cake with powdered sugar and then cocoa powder.
Slice into 1" pieces with a serrated knife and serve. Garnish with mint if desired.