To get a jumpstart on this recipe, make the pastry dough up to 1 day ahead.
Make the pastry:
In a large bowl, whisk together the flour, sugar and salt. Add the chilled butter and use your fingers, 2 forks or a pastry cutter to quickly cut the butter into the flour mixture until it resembles a coarse meal with no large chunks of butter visible. Gradually drizzle the ice water over the mixture and toss lightly with a fork just until the dough holds together when pinched.
Turn the dough out on a work surface. Grab a small clump of dough and use the heel of your hand to quickly press it into the work surface to distribute the fat evenly. Repeat with the remaining dough then gather the dough into a ball, wrap it in a double layer of plastic wrap and refrigerate until chilled, at least 1 hour.
On a lightly floured work surface with a lightly floured rolling pin, roll the dough into roughly 12-inch circle. Place the dough on a rimmed baking sheet and chill until ready to use.
Make the filling:
Preheat the oven to 400°F.
In a large bowl, toss the apple slices with the lemon juice, brown sugar, cinnamon and salt. Arrange the apples in concentric circles on top of the chilled pastry, leaving a 1-inch border. Drizzle the melted butter over the apples then fold the pastry edges up and over the apples to create a 1-inch border.
Bake the galette until the pastry is golden brown, about 1 hour. Transfer to a rack to cool and serve warm or at room temperature.