- ½ vanilla bean or 1 teaspoon vanilla extract
- ¾ cup sugar
- 9 ounces dark bittersweet chocolate (65 to 70 percent cocoa solids)
- 3 eggs, at room temperature
- 1 egg yolk, at room temperature
- 1/8 teaspoon salt
- 12 tablespoons (6 ounces) butter, at room temperature
- 8-inch springform pan or 8 muffin tins
- Preheat the oven to 350°F. Grease and sugar an 8-inch springform pan or 8 muffin tins.
- Make the sugar syrup:
- Using a paring knife, cut down the center of the vanilla bean and scrape out the tiny black seeds into a heavy-bottomed saucepan. Add ½ cup water, the sugar, and the pod to the saucepan and bring to a rolling boil over medium-high heat. Remove the pan from the heat. Allow the syrup to rest for 10 minutes before removing the vanilla bean. Dry the bean and save for another use. (If you are using vanilla extract, you will add it later.)
- Prepare the chocolate sauce (see “Chocolate and water” in the Notes section, below):
- Chop the chocolate into ½-inch pieces and place in a medium-sized bowl. Pour half of the hot vanilla syrup over the chocolate and begin whisking the mixture gently. (The chocolate will seize a bit.) Add the remaining vanilla syrup and continue whisking until you have a shiny, thick chocolate sauce, 2 minutes.
- Add the butter and eggs:
- Add the eggs and egg yolk, one at a time, to the chocolate sauce, whisking after each addition. Whisk in the salt and the vanilla extract if you have not used a vanilla bean in making the syrup. Add the butter, 1 tablespoon at a time. Continue whisking the batter until all the butter is incorporated. The finished chocolate cake batter should be shiny and somewhat viscous. The batter can be made up to this point and refrigerated for up to 3 days.
- Bake the cake:
- If the batter has been refrigerated, allow it to come to room temperature. Scrape the batter into the prepared pan, evening the batter with a rubber spatula. Bake the cake until the center of the cake is set and the top has cracked and developed a glossy, thin crust, 45 to 60 minutes (25 to 30 minutes if you are using individual molds). If the center seems a bit jiggly, bake for another 10 minutes. Remove from the oven and allow to cool for 1 hour before serving.
- Serving Suggestions:
- Serve this cake warm with a dollop of whipped cream, crème fraîche, or vanilla ice cream. I also recommend the Cinnamon Caramel Mousse, Banana Cream, Espresso Ice Cream, Fresh Fig and Madeira Compote, or Rum Caramel Sauce.