Preheat oven to 375 F (190C). Place a baking sheet on the middle rack in the oven.
Grease with butter 4 ramekins of 8 oz (230ml) capacity using a brush and making upward strokes (seems this step help the souffle rise evenly).
Coat the bottom and sides with sugar. Discard excess sugar.
Separate whites from yolks and set aside until ready to use.
In a medium saucepan bring milk to a simmer.
In another saucepan mix yolks with 3 tbsp sugar until slightly pale.
Add flour and whisk to combine.
Pour about a third of the hot milk over the egg yolk mixture to temper the yolks. Add the rest of the milk and return to heat.
Bring to a boil, stirring continuously; cook 1-2 minutes more or until thickened.
Remove from heat and stir in vanilla extract. Transfer mixture to a larger bowl and let cool slightly.
In a separate bowl whip whites with a pinch of salt until foamy. Gradually add remaining 3 tbsp of sugar and continue whipping until stiff peaks form.
Gradually fold the whipped whites into the yolk mixture.
Divide the mixture evenly into the prepared ramekins.
Place the ramekins onto the preheated baking sheet.
Bake for 25-30 minutes until golden and puffed.
Dust with powdered sugar and serve immediately. Enjoy!