Preheat to 400 degrees.
Lightly grease a 17x11 inch jelly roll pan.
Line with waxed paper; grease and lightly flour.

Chocolate Roll:
Melt butter in a small pan and let cool slightly.
In a medium bowl stir together flour, 1/3 c cocoa and baking powder.
In another medium bowl whisk together 5 egg yolks, 1/4 c sugar and melted butter until light, about 1 minute.
Whisk in vanilla.
With a spoon, stir in about half of the dry ingredients.
In a large, deep bowl combine the egg whites and salt.
With an electric mixer, beat until soft peaks just begin to form.
Gradually beat in remaining 1/2 c sugar, beating just until stiff, glossy peaks form.
Fold about 1/4 of the egg whites into the egg yolk mixture to lighten.
Turn this mixture into the bowl of egg whites and partially fold together.
Sift the remaining dry ingredients over the top and quickly and gently but thoroughly fold together until no streaks remain.
Quickly spread in the prepared pan and bake 10 to 12 minutes, just until the center top springs back when lightly touched.
Sift remaining 2 T cocoa onto a clean kitchen towel.
Invert the cake onto it and peel off the paper.
With a long, sharp knife trim away about 1/2 inch from each edge.
Start along one long side, roll up jelly roll fashion.
Wrap in the towel and let cool to room temperature.
While roll cools, prepare the coffee cream.

Coffee Cream:
In a medium saucepan over low heat, scald milk until tiny bubbles appear around the edges of the surface.
Place 1 T cold water in a cup and sprinkle gelatin over it.
Let soften until needed.
In a medium bowl stir together sugar, flour, and salt.
Gradually whisk in scalded milk.
Place in a heavy medium saucepan over moderately low heat.
Stirring constantly, cook until mixture thickens and comes to a simmer.
Whisk in egg yolks and continue cooking and stirring until the mixture comes to a boil.
Remove from heat and stir in the coffee powder and dissolved gelatin until smooth; stir in vanilla.
Turn into a shallow bowl.
Cover with plastic wrap or waxed paper placed directly on surface.
Cool just to room temperature.

Assembly:
Using chilled bowl and beaters, whip the cream until stiff.
Give the coffee cream filling a good stir and fold in about 1/4 of the whipped cream to lighten.
Turn the lightened coffee filling into the whipped cream and fold together.
Carefully unroll the chocolate cake onto a board.
Spread all of the coffee cream over it, making it thicker along the side where you will begin to reroll and leaving about 1 inch uncoated along the other long side.
Reroll the chocolate cake to enclose the filling.
Leave it on the board, seam side down.
Cover and chill overnight.
Trim the ends and cut into slices.
Serve cold.