Heat the oven to 425°F.

In a large heat-proof bowl set over a pan of hot, not simmering water (do not allow the bottom of the bowl to touch the water) place the chocolate and butter and allow it to stand, stirring occasionally, until smooth and melted. (You can also use a microwave on higher power, stirring every 20 seconds.)

In a large mixer bowl, set over a pan of simmering water, heat the eggs, stirring constantly with a wire whisk, until just warm to the touch. Immediately remove the bowl to the stand mixer and with the whisk attachment on high speed, beat about 5 minutes, until triple in volume and the eggs are billowy and lighter in color. (If using a handheld electric mixer, beat the eggs over simmering water until they are hot. Then remove them from the heat and beat for about 5 minutes or until cold.)

Use as large wire whisk or rubber spatula to fold half the eggs into the chocolate mixture until almost evenly incorporated. Fold in the remaining eggs until almost no streaks remain. Use a rubber spatula to finish folding, scraping up the mixture from the bottom to ensure that all the heavier chocolate mixture gets incorporated.

Scrape the mixture into the prepared pan and set it in the larger pan. Place it in the oven and surround it with 1 inch of hot water. Bake for 5 minutes. Cover it loosely with a sheet of buttered foil and bake another 10 minutes. (It will wobble when moved.) Remove the cake pan from the water bath and allow it to cool for about 45 minutes. Cover tightly with plastic wrap and refrigerate it until very firm, at least 3 hours.

Unmold the cake: Have ready a serving plate that has at least an 8-inch flat center portion and an 8-inch or large flat loose bottom of a tart pan or plate, covered with greased plastic wrap.

Use a torch, hair drier, or a hot damp towel to wipe the sides of the pan.

Run a thin metal spatula around the sides of the torte and release the sides of the springform pan. Place the plastic-wrapped plate on top and invert the torte onto it. Heat the bottom of the pan and remove it. Peel off the parchment and reinvert the torte onto the serving plate.

Serve: It is most moussey and delicious at room temperature. Cut the torte, using a thin-bladed knife dipped in hot water between each slice. Accompany with raspberry sauce and fresh raspberries and whipped cream if desired.