In a large bowl, stir together the strawberries, white sugar, cornstarch, and balsamic vinegar. Set the filling aside.
Preheat the oven to 350°F. Line a baking sheet with parchment paper.
Lightly flour your work surface. Remove the dough from the fridge, then using a rolling pin, roll into a 14-inch round. Drape the dough around your rolling pin and transfer it to the baking sheet.
Using a slotted spoon, transfer the filling into the center of the dough, leaving a 2-inch border around the edges. Using your fingers, fold the edges of the dough up and over the filling. Brush the top of the dough with the egg wash, then sprinkle it with sanding sugar if desired.
Bake the galette for 40 to 45 minutes, until the crust is golden brown and the filling is bubbly. (The juices in the galette will thicken as it cools.)
Slice the galette into wedges, then top with whipped cream or ice cream and serve.