Make the blueberry jam
Combine the blueberries, sugar, lemon juice, and vanilla in a saucepan and cook over medium heat. Stir in cornstarch and salt until thickened, then set aside to cool.
Make the blueberry filling
Toss the blueberries, sugar, and cornstarch together.
Roll the galette dough to about 8" in diameter. Spread on about 3 tbsp of the jammy filling, then an even layer of the fresh blueberry filling. Fold the edges of the dough over onto the filling.
Brush the edges of the galette dough with an egg wash and sprinkle with turbinado sugar. Bake them at 400 degrees F for about 30 minutes.
Allow the galettes to cool for a few minutes, then top with vanilla ice cream and enjoy!