Beat the 6 egg whites in a medium bowl until stiff. In a large bowl, beat the 6 egg yolks with the sugar until lemon-colored. Add the flour and baking powder to egg yolks. Then fold egg whites by hand into egg yolk mixture. Pour the batter into a jellyroll pan (14 inches by 16 inches, if you can find one that size) that is greased and lined with waxed paper, cut to size.
Bake in a preheated 350-degree oven for 12 to 15 minutes until lightly browned. Invert on a flat kitchen towel, gently remove the waxed paper, and let cool for about 20 minutes on the counter. Then roll up in a jellyroll fashion, starting at the short end. Let sit for an hour until completely cool before filling and icing the cake.
Melt together the chocolate chips, instant coffee, and water, stirring until smooth. Set aside to cool completely.
Whip the cream or non-dairy substitute until stiff. Add 1/3 of the chocolate mixture and blend. Unroll cake, cover completely with filling, and then roll back up. Use a large spatula (or two smaller ones) to move the cake to a serving platter.
To remaining chocolate mixture, add the melted butter or margarine and stir until well mixed. Spread over the cooled cake as icing.
If desired, toast blanched and slivered almonds and sprinkle on top of the iced cake.
This cake can be completely made, frosted, and frozen for use later. Defrost in the refrigerator before serving.
Adele Fleet Bacow is president of a community planning consulting firm, mother of two great sons, and the First Lady of Tufts University (her husband Larry is the President). She is also a very good cook and a great friend to the Food Editor.