Preheat the oven to 350°F.

In the top of a double boiler, melt the chocolate in the coffee over simmering water. Stir until smooth.

Butter a 10 X 15-inch jelly roll pan. Line with parchment paper. Butter the paper.

Beat the egg yolks until fluffy. Add the sugar gradually and beat until very thick. Beat in the chocolate mixture and salt.

Beat the egg whites until stiff. Carefully fold into the chocolate mixture. Spread evenly in the prepared pan.

Bake the cake for 12 to 15 minutes, until it springs back when gently touched in the center. Remove from the oven and place on a rack. Cover the cake with a damp kitchen towel and a piece of plastic wrap, and let cool for 1 hour.

Remove the towel and sprinkle the cake with the cocoa. Cover with a large piece of parchment paper and place a flat baking sheet over the paper. Invert the cake and carefully peel away the parchment the cake baked in.

Whip the cream until stiff. Spread half of it over the cake. Carefully roll the cake from one long side, lifting the parchment paper to get it started. Place the roll seam-side down on a serving tray. Ice the cake with the remaining cream and chill.