In a large bowl, mix the washed blueberries with the sugar, the corn starch and the lemon juice. Set aside.
Roll the ball of pie crust on a floured surface about 1/4 of an inch thick (0.5cm).
Pour the blueberry mixture onto the pie crust and fold back the edges to cover some of the blueberries.
Brush the edges of the blueberry galette with egg wash and sprinkle some sugar on top.
Bake for 30 to 40 minutes a 350F.