Serves 6 to 8.
8 tablespoons (1 stick) unsalted butter, cut into pieces
6 ounces bittersweet chocolate, chopped
3/4 cup plus 2 tablespoons granulated sugar
1/2 cup all-purpose flour
3/4 teaspoon baking powder
1/8 teaspoon salt
4 large eggs
1 teaspoon pure vanilla extract
Melt the butter and chocolate in a double boiler or a metal bowl set over simmering water, stirring occasionally. Allow the mixture to cool to room temperature.
Preheat your oven to 325 degrees F.
Sift the sugar, flour, baking powder, and salt together and set aside. Beat the eggs and vanilla in a medium bowl until frothy. Stir in the chocolate mixture until incorporated. Then slowly stir in the sugar-flour mixture just until everything is combined.
Divide the batter among six 6-ounce or eight 5-ounce custard cups or ramekins. Arrange the custard cups in a baking dish or roasting pan and fill the dish with enough cool tap water to come one-third of the way up the sides of the cups. (This water bath assures that the bottom portions of the cakes remain in a batter state.)
Bake for 34 to 38 minutes, until the tops are firm. Serve warm.