Prepare the Crust:
In a large bowl, whisk together flour, sugar, and salt.
Add the cold, cubed butter. Using a pastry blender or your fingers, cut the butter into the flour until the mixture resembles coarse crumbs.
Gradually add ice water, one tablespoon at a time, mixing gently after each addition until the dough just comes together to form a ball.
Form the dough into a disc, wrap it tightly in plastic wrap, and refrigerate for at least 30 minutes, or up to an hour.

Blind Bake the Crust:
Preheat your oven to 375°F (190°C).
Roll out the chilled dough on a lightly floured surface into a circle about 12 inches in diameter.
Carefully transfer the dough to a 9-inch tart pan with a removable bottom. Press the dough into the pan and trim any excess. Crimp the edges for a decorative border.
Line the crust with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes.
Remove the parchment paper and pie weights, then bake for an additional 10-15 minutes, or until the crust is lightly golden. Let the crust cool completely.

Make the Lemon Filling:
In a medium saucepan, whisk together sugar, cornstarch, and salt.
Gradually add water and lemon juice, whisking until smooth.
Bring to a simmer over medium heat, stirring constantly until the mixture thickens.
In a small bowl, lightly beat the egg yolks. Gradually whisk in a small amount of the hot lemon mixture to temper the yolks.
Pour the tempered egg yolks into the saucepan, stirring constantly. Cook for 1-2 minutes until the mixture is thick and glossy.
Remove from heat, then stir in butter, lemon zest, and vanilla extract. Let the lemon filling cool slightly before pouring it into the cooled crust.

Prepare the Blueberry Topping:
In a medium bowl, gently toss the fresh blueberries with sugar, lemon juice, and lemon zest.
Arrange the sugared blueberries evenly over the cooled lemon filling in the tart shell.

Chill the Tart:
Cover the tart with plastic wrap and refrigerate for at least 2 hours, or preferably overnight, to allow the filling to set.

Serve and Garnish:
Before serving, dust the tart with powdered sugar and garnish with fresh mint sprigs for a touch of color and freshness.
Slice and serve chilled.