Preparation :

Pile the flour on the work surface and dig a fountain in the middle.  Sprinkle the salt on the edges of the fountain.
Dissolve the yeast in a tablespoon of warm milk.  Add this yeast in the fountain with a little sugar.  Cover with flour to allow it to rise.
Beat the egg and add it to the fountain as well as the warm milk and oil.  Knead the dough by hand mixing all the flour gradually until the dough is smooth.  Fold the dough with your fingertips to incorporate air (in the same way as when kneading bread dough).  Add the softened butter and stir it in.  Knead the dough, preventing it from hardening.
Leave it to rise for 30 minutes at low heat.  With a rolling pin, flatten the ball of dough and place it in a greased dish, adjusting the fit with your fingers.  Prick the base of the tart with a fork.  Leave the dough to rise for about another fifteen minutes.  Before putting on the garnish, brush the pastry with unbeaten egg white.
Spread out a generous layer of blueberries.  Place the pie in middle of oven for 15 to 20 minutes, thermostat 250°C.  Check that the tart is cooked by lifting the tart from the dish.  Let it cool and sprinkle with sugar.