Preheat the oven to 350 degrees F. Butter a 9-inch spring-form pan.
Put the chocolate and butter into the top of a double boiler (or in a heatproof bowl) and heat over (but not touching) about 1 inch of simmering water until melted. Meanwhile, whisk the egg yolks with the sugar in a mixing bowl until light yellow in color. Whisk a little of the chocolate mixture into the egg yolk mixture to temper the eggs- this will keep the eggs from scrambling from the heat of the chocolate - then whisk in the rest of the chocolate mixture.
Beat the egg whites in a mixing bowl until stiff peaks form and fold into the chocolate mixture. Pour into the prepared pan and bake until the cake is set, the top starts to crack and a toothpick inserted into the cake comes out with moist crumbs clinging to it, 20 to 25* minutes. Let stand 10 minutes, then remove sides of pan.
While the cake is cooking, whip the cream until it becomes light and fluffy. (I added a splash of vanilla extract to the whipped cream.)
Serve at room temperature dusted with confectioners’ sugar and topped with whipped cream.
*adapted from Tyler Florence’s recipe. (I actually baked about 20 minutes longer than the suggested time, taking me to about 40 minutes. This yielded a lovely, springy, and moist cake.) Serve this at your next dinner party!