For the raspberry sauce:
- 2 1/2 cups fresh raspberries or thawed frozen unsweetened raspberries
- 1/2 cup superfine sugar
- 1/4 cup framboise or other raspberry-flavored liqueur (optional)
For the cake:
- 1 lb. semisweet or bittersweet chocolate, chopped
- 10 Tbs. (1 1/4 sticks) unsalted butter, at room temperature
- 4 extra-large eggs, at room temperature
- 1 Tbs. sugar
- 1 Tbs. all-purpose flour
- 1 cup heavy cream, whipped
To make the cake, position a rack in the middle of an oven and preheat to 425ºF. Butter an 8 or 9-inch springform pan or a layer cake pan. Line the bottom with a circle of parchment paper or waxed paper cut to fit precisely. Butter the paper and dust with flour; tap out any excess.
Place the chocolate and butter in a large heatproof bowl or the top pan of a double boiler. Set over a pan of gently simmering water but not touching the water. Stir occasionally until melted and combined completely. Remove from the heat and let cool slightly.
Place the eggs and sugar in a bowl. Using an electric mixer set on high speed, beat until light, fluffy and tripled in volume, 5 to 10 minutes. Reduce the speed to low and beat in the flour. Using a rubber spatula, fold one-third of the egg mixture into the chocolate to lighten it, then fold in the remaining egg mixture, taking care not to deflate the batter. Pour and scrape the batter into the prepared pan and smooth the top.
Bake for exactly 15 minutes. Let cool completely to room temperature. Do not refrigerate or the cake will stick to the pan. Invert the cake onto a flat serving plate and peel off the paper.
Cut into small wedges and serve each wedge atop some of the raspberry sauce. Top with whipped cream.