
Butter, for greasing
Granulated sugar, for coating dishes
4 ounces bittersweet chocolate, finely chopped
⅓ cup unsweetened Dutch-process cocoa powder
¾ cup granulated sugar, divided
⅓ cup boiling water
2½ teaspoons vanilla extract, divided
4 large egg yolks
2 tablespoons all-purpose flour
6 large egg whites, at room temperature
½ teaspoon cream of tartar
½ cup whipping cream
1 tablespoon packed brown sugar