Preheat the oven to 400 degrees and then line a baking sheet with parchment paper. Set aside.
In a medium mixing bowl, combine blueberries (be sure to rinse them first), granulated sugar, lemon juice, lemon zest and vanilla. Mix well and set aside.
Unroll the dough onto the parchment paper.
Mix the filling again. Spread the filling in the center of the dough, leaving about an inch space uncovered around the edges.
Fold edges of the dough up over the blueberries, pinching the dough in the overlap areas. This will prevent the overlap area from coming apart. Optionally, you can brush some of the egg wash over the area to be overlapped. The egg wash acts like glue.
To get a really nice golden and shiny crust, beat 1 egg. Then brush the dough with the egg wash.
Sprinkle some vanilla sugar all over the folded edges of galettes.
Bake for 20-25 minutes or until the crust is golden.