Heat oven to 400℉.
Butter inside of soufflé dishes and coat with sugar, making sure to bring butter and sugar all the way to the top of the rim of the ramekin. Set aside.
In a small saucepan, melt butter.
Whisk in flour. Set aside.
Heat milk and 4 teaspoons sugar until sugar dissolves.
Bring to a simmer.
Remove from heat.
Whisk into flour mixture.
Return to heat.
Cook over medium-low heat, whisking continually, until it achieves a pudding-like consistency, about 3-5 minutes.
Transfer to clean bowl.
Cover and let cool for 3-5 minutes.
While mixture is cooling, place chocolate in a small microwave safe bowl.
Microwave in 10-15 second increments, stirring well after each, until chocolate is melted and smooth.
Stir into milk mixture.
Whisk in egg yolks and vanilla.
Whip egg whites to soft peaks.
Add 1/2 teaspoon sugar.
Beat to stiff peaks, being careful not to over beat.
Fold into chocolate base.
Divide into prepared ramekins.
Smooth out the top.
Bake for 15 minutes, until puffed and done.
Lightly sprinkle tops with powdered sugar.
Serve immediately.