Line a baking sheet with parchment paper, then lay the sheet of puff pastry onto the pan.
Place a saucepan over medium heat. Add 2 cups of the sliced strawberries to the pan, along with maple syrup, sugar, orange zest and vanilla extract.
Cook for about 8-10 minutes, or until the sugar has melted and strawberries have begun to break down.
In a small bowl, mix cornstarch with 1 tbsp of water. Once combined, add to the strawberry mixture and continue to cook until the mixture has thickened.
Remove the pan from the heat. Allow mixture to cool for 10 minutes.
Meanwhile, fold up the sides of the pastry into a 2-inch border.
Add the cooked strawberry mixture to the pastry. Top with remaining raw strawberries. Adjust the edges of pastry if needed.
Brush the pastry with milk, and sprinkle coarse sugar (if using) over the entire galette.
Bake for 18-20 minutes, or until the pastry is golden brown and puffed up.
Serve warm or at room temperature, with ice cream or whipped cream.
If you can't find pre-rolled puff pastry, you can thaw a square of puff pastry and roll it out on a floured surface. Be careful not to make the dough too thin or it may rip. Please note that the nutritional information for this recipe is only an estimate, and has been calculated using a plugin.