In a medium bowl, stir together the flour, salt, and sugar. Using a pastry cutter or your fingers, cut in the cubes of butter until they are crumbly and pea sized.
Mix in the ice cold water one tablespoon at a time, stirring with a spoon until a cohesive ball of dough forms. It is ready when the dough can hold together on its own but it will still have some crumbly pieces. Wrap in plastic wrap or a clean towel and let rest in the fridge for 30 minutes.
For the berries
In a medium bowl, combine the berries, sugar, corn starch, and lemon juice. Let sit for 15 minutes.
After 15 minutes, transfer the berries to a strainer to strain off any liquid.
On a baking mat or lightly floured surface, roll out the dough until it is roughly 12x12 inches. It does not need to be a perfect circle.
Transfer the dough to a parchment paper lined baking sheet (parchment paper is optional but makes cleanup easier). Place the berry mixture in the center, leaving two inches of dough uncovered around the outside.
Fold the dough in over the berries, pinching any overlapping edges together as needed.
Optional: Make an egg wash by whisking together one egg yolk with 1 tablespoon milk (water works in a pinch). Brush it on the edges of the pie crust. Sprinkle with coarse sugar. This will make the crust golden and sweet.
Bake at 425F for 25-30 minutes, until the crust is golden and the berry mixture is bubbling.
Let the galette cool on a cooling rack for at least an hour before slicing. Serve with vanilla ice cream (optional but delicious).
Berries: Any mixture of berries works. Aim for around 3 cups. If using frozen berries, make sure they are completely thawed. Frozen berries won't keep their color as well as fresh and usually result in a blue/purple galette.
Galette dough: Storebought pie crust can be used to cut down on prep time.
Leftovers: Store leftovers in the fridge for 3-4 days.