Preheat the oven to 400 degrees F. Butter 8 (1/2 cup) ramekins or custard cups with 2 tablespoons butter. Set aside.
For the souffles: Stir the chocolate and 6 tablespoons butter in a large metal bowl set over saucepan of simmering water until the mixture is melted and smooth (mixture will be a little grainy). Remove the chocolate mixture from the heat and let cool slightly. Whisk in the egg yolks and add 2 tablespoons of the cooled melted chocolate to the yolks, mixing to incorporate. Add the rest of the chocolate and mix until nice and smooth. Using an electric mixer, beat the egg whites in a medium bowl until foamy. Add the sugar and beat until stiff peaks form. Fold into the chocolate mixture in 3 additions. Divide the chocolate batter among the prepared ramekins, filling them three-quarters of the way.
Bake the souffles until puffed but the centers jiggle slightly, 16 to 18 minutes. Serve immediately.