Preheat the oven to 375°F. Grease 4 ramekins with butter, then coat with granulated sugar. Shake out any excess.
In a small saucepan over medium heat, whisk the flour and milk until smooth and thick, about 2 minutes.
Remove from heat and stir in the vanilla. Let cool for a minute, then whisk in the egg yolks.
In a separate bowl, beat the egg whites with cream of tartar until soft peaks form. Gradually add sugar and beat until glossy stiff peaks form.
Gently fold a third of the egg white mixture into the yolk mixture to lighten it, then fold in the remaining whites carefully.
Spoon the batter into the ramekins, smooth the tops, and run your thumb around the inside edge to help them rise evenly.
Bake for 12-14 minutes until puffed and golden. Dust with powdered sugar and serve immediately before they deflate like my motivation on Monday mornings.