Preheat oven to 425 degrees.

In a bowl, combine blueberries, sugar, cornstarch, lemon zest, lemon juice, vanilla, and salt.

Set the blueberry mixture aside.

Unroll the pie crust dough.

Cut out six 5-inch rounds from the dough.

Place the dough rounds on baking sheets lined with parchment paper.

Distribute the blueberry mixture evenly among the dough rounds (about 1/4 cup each).

Fold the edges of the crust over the filling, creating a small rim.

In a small bowl, whisk together the egg and water to make an egg wash.

Brush the edges of the crust with the egg wash.

Sprinkle the crust with sugar.

Bake for 15 minutes, or until golden and bubbly.

Let the galettes cool on the pan for 5 minutes.

Transfer to a platter to cool completely.

Serve warm or at room temperature with whipped cream.