In a big bowl, put in the flour, sugar, and salt. Mix them together. Now, add the cold butter cubes. Using your fingers or a pastry blender, work the butter into the flour until it looks like coarse crumbs.

Slowly pour in the ice water, one tablespoon at a time. Mix gently until the dough just comes together. Form the dough into a flat disc shape, wrap it up in plastic wrap, and pop it in the fridge. Let it chill for at least 30 minutes.

In another large bowl, gently put in the fresh blueberries, sugar, cornstarch, lemon juice, and cinnamon. Mix everything together softly until all the blueberries are coated with the mixture. Set this bowl aside for now.

Sprinkle a little flour on your kitchen counter or a clean board. Take the chilled dough out of the fridge and unwrap it. Use a rolling pin to roll the dough into a circle that’s about 12 inches wide and about 1/8 inch thick. Carefully lift the dough and place it into a 9-inch tart pan that has a removable bottom. Gently press the dough into the pan, making sure it fits snugly into the corners and up the sides. Trim off any extra dough that's hanging over the edge of the pan. You can make the edges look pretty by crimping them with a fork, or just leave them plain.

Pour the blueberry filling right into the tart crust. Spread it out evenly. Put the tart in a preheated oven at 375°F (190°C) for about 45-50 minutes. You’ll know it’s done when the crust is golden brown and the blueberry filling is bubbly.

Once your French Blueberry Tart is baked, take it out of the oven and let it cool completely in the tart pan on a wire rack.