Add the flour and salt to the bowl of a food processor. Pulse a few times to combine.Add the cold, cubed vegan butter to the food processor. Pulse the mixture several times until it resembles coarse crumbs with some larger pea-sized pieces of butter remaining.
Gradually add 2 tablespoons of ice water through the feed tube while pulsing the processor. Continue to add ice water, 1 tablespoon at a time, pulsing after each addition, until the dough begins to clump together. The dough should hold together when you pinch it between your fingers. Be careful not to add too much water.
Turn the dough out onto a clean surface. Gather it into a ball and then flatten it into a disk. Wrap the disk in plastic wrap and refrigerate for at least 30 minutes, or up to 2 days. Chilling the dough allows the butter to firm up, which helps create a flaky crust.
When you're ready to make the galette, remove the dough from the refrigerator and let it sit at room temperature for about 5-10 minutes to make it easier to roll out. On a lightly floured surface, roll the dough into a rough circle, about 1/4-inch thick. If the dough cracks or breaks, gently press it back together.
To make the filling:Preheat the oven to 375 degrees. Line a baking sheet with parchment paper. Add the blueberries, granulated sugar, cornstarch and lemon juice to a mixing bowl. Toss to combine.
Add the filling to the middle leaving a 2-3 inch boarder all around.
Fold the edges of the dough over and brush them with agave to turn them golden brown. Bake for 45-50 minutes or until the edges are golden brown. Remove from the heat and let cool. The filling will firm as it cools down. Serve with vegan vanilla ice cream and enjoy!