Preheat oven to 350° F. Line a medium (5 or 6 cup, or about 8-inches diameter) stainless steel bowl with aluminum foil so the foil overlaps the bowl by 3 to 4 inches.
Put the chocolate pieces in a saucepan. Pour the hot coffee over it, which will melt some of the chocolate. Place over medium-low heat; add the sugar and stir with a wire whisk to dissolve the sugar and any unmelted chocolate. Add the butter gradually, a dollop at a time, whisking until the butter is incorporated before adding the next dollop. This should take about 10 minutes. Remove from heat.
Slowly whisk the beaten eggs into the chocolate mixture. Pour through a strainer into the foil lied bowl to eliminate any firm bits of egg. Bake 50 to 55 minutes, until the batter rises and a cracked top crust forms. The mixture will still jiggle, like molded gelatin. Resist the urge to bake it al little more; the butter and chocolate firm up when chilled.
Let the cake cool. Fold the overlapping foil over the top and refrigerate at least 8 hours, keeping the cake in the bowl. It will keep up to a week if refrigerated and well-wrapped in plastic wrap. The cake can also be frozen for up to a month; thaw in the refrigerator before frosting.
Pull the overlapping foil away from the cake; it will have fallen in the center. Press the edges down to make what will be the bottom of the cake even, or cut the edges off with a knife (save for snacking.) Place a flat plate or cardboard circle over the bowl, invert, and gently remove the rest of the foil.
Whip the cream with the sugar and vanilla until the cream comes to soft peaks that hold their shape. Put the cream in a pastry bag fitted with a large star tip; pipe stars all over the cake. You can decorate the cake with edible flowers if you wish. If you aren't going to serve it immediately you might consider using a pastry cream, to keep the whipped cream from separating and running later.Makes 6 Source: