1. Preheat oven to 180°C.
2. Coat 2 ramekins with butter, sprinkle each with 3/4 teaspoon granulated sugar.
3. Combine 2 tbsp granulated sugar, flour, cocoa, and milk in a small saucepan over medium heat. Cook 2 minutes, stirring until smooth. Spoon chocolate mixture into a medium bowl and cool 4 minutes. Stir in vanilla.
5. Place egg white in a medium bowl, beat with a mixer at high speed .
6. Add remaining 2 tbsp granulated sugar, beating until stiff peaks form. Gently stir 1/4 of egg white mixture into chocolate mixture, gently fold in remaining egg white mixture.
7. Spoon mixture into prepared dishes. Sharply tap dishes 2 or 3 times to level.
8. Place dishes on a baking sheet and bake for 15 min.
9. Sprinkle each soufflé with 1/2 teaspoon powdered sugar.