To make the cake, sift the flour, cocoa, and salt together into a small bowl. In a separate bowl, beat the egg whites until frothy. Add the cream of tartar and beat until stiff peaks form. Gradually beat in half the sugar. Combine the egg yolks, the remaining sugar, and almond extract in another bowl and beat until thick and pale yellow. Stir in the sifted flour and cocoa mixture. Fold in the egg white mixture, being careful not to over mix. Grease a 9 x 13-inch jelly-roll pan, line the bottom with wax paper or parchment, and grease the paper. Transfer the batter to the prepared jelly-roll pan and smooth to level the top. Bake in a preheated 350 F oven for 15 to 20 mins, until the cake is spongy to the touch. Have ready a large piece of wax paper liberally dusted with confectioner's sugar, and transfer the cake, upside down, to the dusted paper. Remove the wax paper that was lining the pan from the bottom of the cake and roll the cake up with the dusted wax paper still inside. Set aside.

To prepare the filling, combine the rum and gelatin in a small cup and let soak for 10 mins. Melt the chocolate in a pan over simmering water. With the pan still over the simmering water, stir the gelatin mixture into the chocolate and, using an electric beater, whip in the sugar and chestnut puree. Remove from the heat and let cool to room temp.Whip the cream until soft peaks form and fold into the chestnut mixture.Unroll the cake carefully and spread it with half the chestnut mixture. Roll it up again, removing the wax paper this time, and place on a serving dish. Cover with the remaining chestnut mixture and score with the tines of a fork to make a pattern resembling the bark of a tree. Refrigerate until ready to serve. Garnish with a dusting of cocoa powder immediately before serving. Decorate the plate with sprigs of holly if desired.
Serves 6 to 8.