HEAT oven to 325ºF.
BEAT egg white and sugar in small bowl with mixer on high speed 1 to 2 min. or until stiff peaks form; set aside.
MELT butter in small saucepan on medium heat. Stir in flour until well blended. Add milk; cook and stir 30 sec. or until thickened. Remove from heat. Add chocolate; stir until melted. Add egg yolk to mixture; mix well. Gently stir in egg white just until blended.
POUR into 2 (6-oz.) ramekins; place on baking sheet,
BAKE 30 to 32 min. or until soufflés are puffed and centers are set. Serve immediately.