- Unsalted butter, for pan
- 1 1/2 tablespoons instant espresso powder
- 6 tablespoons hot water
- 24 ounces semisweet chocolate, coarsely chopped
- 6 tablespoons dark rum
- 9 large eggs
- 3/4 cup granulated sugar
- 1 1/2 cups heavy cream
- 1 tablespoon confectioners' sugar
- 1 tablespoon pure vanilla extract
- Sweetened whipped cream, for garnish (optional)
Preheat oven to 350 degrees. Place a large roasting pan in the oven, and fill 1 inch with boiling water. Butter a 10-inch heart-shaped pan 2 inches deep. Line with parchment paper; set aside.
In a small bowl, combine the espresso and water. Stir to dissolve. In a heatproof bowl, combine the chocolates, espresso mixture, and rum over a saucepan of simmer water. Stir until smooth. Remove, and set aside.
Over the same saucepan of simmering water, combine the eggs and granulated sugar in a large heatproof bowl. Beat, using a handheld electric mixer, until thick, fluffy, and almost tripled in volume.
Whip the cream in a chilled bowl until soft peaks form. Add the confectioners' sugar and vanilla.
Fold the melted-chocolate mixture into the egg mixture. Gently fold in the whipped cream. Transfer to prepared pan. Immediately set the pan in the roasting pan with hot water in the oven. Bake until a toothpick inserted in the center comes out clean, about 1 hour.
Remove from oven, and let cool in the water bath. When cool, cover, and refrigerate overnight.
Just before serving, uncover the pan, and warm slightly in an inch of warm water to loosen from pan. Invert onto a platter. Pipe the sweetened whipped cream onto the chocolate heart with a decorative tip, if desired.