Make pie dough the night before because it needs to chill in the refrigerator for at least 2 hours before using.
Line two large baking sheets with parchment paper or silicone baking mats.
Gently stir the berries, cornstarch, sugar, and lemon juice/vanilla together in a medium bowl until combined. Place in the refrigerator.
Working with 1 chilled pie dough at a time, roll into a large 12-inch circle. Cut rounds using a 5.5 or 6 inch cookie cutter.
Arrange dough rounds on prepared baking sheets. Spoon about ¼ cup into the center of each dough round, leaving any excess juice behind.
Gently and tightly fold the edges over the filling leaving the very center exposed.
Brush the edges of the pie dough with milk. If desired, sprinkle with coarse sugar and/or sliced almonds/nuts.
Chill the shaped galettes in the refrigerator for at least 20 minutes and up to 4 hours.
Preheat oven to 375°F (191°C).
Bake chilled galettes for 25-28 minutes or until the edges are lightly browned.
Remove from the oven and cool for at least 5 minutes before enjoying.
