Separate egg; let stand at room temperature for 30 minutes. Coat two 6-oz. ramekins with 1 teaspoon butter and sprinkle with 2 teaspoons sugar. Place ramekins on a baking sheet; set aside.
In a small saucepan over medium heat, melt remaining butter.
Stir in 2 tablespoons sugar and the flour until smooth. Gradually whisk in milk. Bring to a boil, stirring constantly. Cook and stir 1-2 minutes longer or until thickened. Whisk in the chocolate, cayenne and salt until chocolate is melted. Transfer to a small bowl.
Stir a small amount of hot mixture into egg yolk; return all to the bowl, stirring constantly. Cool slightly.
In another bowl, with clean beaters, beat egg white on medium speed until soft peaks form. Gradually beat in remaining sugar on high until stiff peaks form.
With a spatula, stir a fourth of the egg white into chocolate mixture until no white streaks remain. Fold in remaining egg white until combined. Transfer to prepared ramekins.
Bake at 400° for 12-15 minutes or until the tops are puffed and centers appear set. Serve immediately. If desired, dust with confectioners' sugar.