Preparation

Make the soufflés

• Brush eight 6-oz. straight-sided ramekins with the butter and coat evenly with 2 Tbs. of the sugar, tapping out the excess. Set aside.

  In a 2- to 3-quart saucepan, heat the milk over medium-high heat until steaming hot. Add the chocolate and stir with a rubber spatula until melted. Transfer the chocolate mixture to a large bowl and set aside.

  Combine the remaining 1/2 cup sugar and 2 Tbs. water in a 2-quart saucepan and set over medium heat, stirring frequently, until the sugar is completely dissolved. Let sit at room temperature while you whip the egg whites.

  In a stand mixer fitted with the whisk attachment, whip the whites on medium speed until soft peaks form, about 3 minutes. With the mixer running, slowly pour the sugar syrup down the side of the bowl into the whites. Increase the speed to high and beat until the whites hold medium peaks, about 1-1/2 minutes.

  Mix the egg yolks into the melted chocolate until combined. Fold one-third of the whites into the chocolate mixture until totally combined. Add the remaining two-thirds of the whites and fold until no streaks remain. Divide the batter evenly among the prepared ramekins. Freeze until solid, at least 8 hours ahead, then wrap tightly with plastic wrap. (The soufflés may be made to this point up to 1 week ahead.)

Bake the soufflés

• When ready to serve, position a rack in the top third of the oven and heat the oven to 375°F. Remove the ramekins from the freezer and bake until the tops are puffed and cracked (either at the edges or on top) and the soufflés are barely set in the middle, 18 to 20 minutes.

Make the whipped cream

• While the soufflés are baking, in a medium bowl, whip the cream using a hand mixer on medium speed until thickened enough to hold very soft peaks. Add the brown sugar, rum, and vanilla and continue to mix until soft peaks form.

  Serve the soufflés, topped with dollops of whipped cream, immediately after baking.