Mix the flour, sugar, salt and baking powder using a whisk.
In another bowl, whisk together the milk, vanilla, butter and egg yolks. When separating the eggs, transfer the yolks straight into the milk so that it doesn't generate a skin, which happens when it's in contact with air.
Make a hole at the centre of the dry ingredients and pour the liquids into it. Whisk them together starting at the centre and slowly incorporating the dry ingredients from the sides.
Whip up the egg whites in a clean using an electric mixer or by hand with a clean whisk until you get soft peaks.
Incorporate the egg whites by folding them in using a spatula.