Making the Dough

1. Place your butter in the freezer for 5 minutes to firm up. Whisk your flour and salt together in a medium-sized bowl. Take your butter out of the freezer, cut it into 1/2 inch cubes, then toss those in your flour to coat. Squish each piece between two fingers to create flat little “shingles” of butter and then use both hands to crumble some of them into smaller pea-sized pieces.
2. Make a well in the center and add 4 tablespoons of ice water. Toss it with the flour until mostly incorporated and then add more ice water by the tablespoon until the dough is shaggy, but generally holds together (not wet and sticky—try not to overwork the dough). Shape into a disc, wrap tightly in plastic, and chill in the fridge for 30 minutes.
3. After it’s chilled, roll out the dough on a lightly floured surface into an ~8×8 inch square (doesn’t have to be exact, just a larger square). Fold in half twice (top to bottom, left to right) so it’s a quarter of the original size. Roll it out and repeat the folds again, using more flour as needed. Wrap tightly in plastic and chill in the fridge for another 30 minutes, up to 1 hour (which is best if you have the time).

Assembling & Baking the Galette

1. In a medium-sized bowl, toss together your blueberries with the sugar and vanilla bean paste (if using). Lightly whisk your egg in a small bowl. Also, prep a large baking sheeting with parchment paper. Set all of these aside.
2. Roll out the dough on a lightly floured surface until about a 1/4 inch thick and cut out a rough circle 10″ in diameter (turn a pie dish upside down and cut around the outside if you want a perfect circle). Place your disc onto your prepared baking sheet. Brush around the outside edge with the egg wash (a good 2 inches) and fill the middle evenly with your blueberry mixture. Working clockwise, fold the crust overtop the blueberries, overlapping the dough as you go (mine usually overlaps 4 or 5 times).
3. Chill in the fridge (on your baking sheet) for 30 minutes to let the dough firm back up. Preheat the oven to 400°F in this time. Then, brush the crust generously with your egg wash and sprinkle with crunchy demerara/turbinado sugar. Bake for 40-45 minutes on the middle or upper rack until your filling has thickened (it will thicken more as it cools down) and crust is to your liking (I like it dark).
4. Let cool on the baking sheet for 15-20 minutes before carefully transferring to a separate rack to cool a bit more. Serve warm as-is or with some ice cream!

Best enjoyed same-day. If you want to break up the process to make it more manageable, you can make the pie dough ahead of time—it’ll keep in the fridge for up to 3 days.