Separate the eggs, including the extra egg white. Set the egg whites aside in a mixing bowl and allow them to reach room temperature.

Combine the yolks and sugar and beat until thick and light colored, about three minutes with an electric mixer on high.

Grate the chocolate and into the top of a double boiler; add the coffee and melt over simmering water. Let cool.

Add the vanilla to the egg-yolk mixture; stir in the chocolate.

Beat the egg whites until stiff peaks. Fold gradually into the chocolate mixture.

Line a jelly roll pan (or cookie sheet) 11x16 inches with wax paper. Generously butter the wax paper and dust lightly with flour. Pour in the batter, smoothing the surface.

Bake in a 300º oven for 15 minutes. Turn off the heat and leave in the oven for an additional 8 minutes.

For the filling: combine the cream, sugar and cocoa in a mixing bowl and let sit in the refrigerator.
Remove the cake from the oven and cover with a cotton cloth that is wet with cold water then wrung out. (The damp towel is key!)
When the cake cools completely, remove the cloth and run a a knife around the side edges of the pan to loosen the cake. Dust the top generously with cocoa.

Turn it onto a work surface lined with wax paper. Remove the wax paper on which the cake baked.

Beat the cream mixture until stiff peaks form. Add flavoring such as vanilla extract or cointreau. Spread the filling on top of the cake, leaving an inch border all around. Roll up the cake lengthwise. Dust the top with cocoa to repair any tears.