Heat the oven to 350°F. Cut parchment paper to fit a sheet pan, butter it, and put the paper in the pan.
Boil a pot of water and lower to a simmer. Put
Whip the egg whites and salt together until soft peaks are formed. While continuing to whip, sprinkle in the sugar gradually and then whip the egg whites to stiff peaks and until the sugar is dissolved, about 5 more minutes. Be careful not to overwhip. Fold the egg white mixture quickly but thoroughly into the chocolate mixture. Spread the mixture in the sheet pan.
Bake until the pastry is firm and has risen evenly, about 20 minutes. Let cool (it will fall as it does so).
While the cake is cooling, make the chocolate cream. Heat the cream in a large saucepan and remove from the heat just before it boils. Chop the remaining chocolate into small bits, add to the hot cream, and stir until the chocolate melts. Strain and set aside to cool until it is just warm.
To assemble the chocolate paradise, remove the chocolate pastry from the sheet pan and remove the paper. Cut into 3 even rectangles just smaller than the loaf pan. Line the bottom and sides of the loaf pan with parchment paper. Pour in a quarter of the chocolate cream, then place a layer of the chocolate pastry on top. Repeat the layers, ending with cream. Refrigerate until the chocolate is set, about 3 hours.
To unmold, dip the loaf pan in hot water for a few seconds to release the edges and then turn over onto a plate.
To serve, cut the chocolate paradise into ½-inch-thick slices. Serve on the mousseline and drizzle with warmed chocolate sauce.
© 1986 Jeremiah Tower. All rights reserved.