1) Preheat oven to 180C/Gas 4. Place blueberries in the bottom of a small rectangular glass pan (about 20 by 25cm).
2) In a medium bowl, crack eggs and whisk lightly. Add sugar and continue whisking until mixture thickens and is pale yellow. Add milk and vanilla; whisk to combine. Add flour and whisk to combine. Add a pinch of fine salt and whisk to incorporate. Pour mixture over the berries.
3) Bake on the centre rack of the oven until the clafouti has puffed and the centre bounces back when lightly pressed, about 45 mins, rotating once.
4) Remove from oven and let cool slightly before cutting. Slice into 8 equal pieces and gently remove from pan with a spatula or cake slice.
5) Dust with icing sugar and serve immediately.