Heat the oven to 190 C Gas 5. Generously grease a 20×25 cm rectangular ovenproof dish, or a 25 cm round one.
Sift the flour and salt into a large mixing bowl and stir in the caster sugar. Beat together the eggs and the egg white.Pour into the centre of the flour and whisk in, gradually incorporating the flour from the sides.
Slowly add the milk, whisking continuously , until you have a smooth batter.
Spread the blueberries quite evenly into the dish, then pour over the batter.
Bake for 35 minutes until puffed up and golden brown.
Serve warm, or at room temperature, dusted with the icing sugar.Accompany with double cream for pouring.