1 and 1/4 cups flour
1 tablespoon sugar
1/4 teaspoon salt
1/2 cup cold unsalted butter, cut into pieces
5 tablespoons very cold water
3 Granny Smith apples, peeled, cored, and sliced
2 tablespoons flour
juice of 1/2 a lemon
1/4 cup granulated sugar
1/4 cup firmly packed brown sugar
1/8 teaspoon salt
6 tablespoons unsalted butter
Make the crust: In a medium bowl, stir together the flour, sugar, and salt. Cut in the butter using two knives or a pastry cutter. Add water and mix with a fork until dough pulls together. Shape into a disc, and wrap in plastic wrap. Store in refrigerator until ready to use.
Preheat oven to 375 degrees.
In a large bowl, stir together the apples, flour, lemon juice, granulated sugar, brown sugar, and salt.
Roll out pie crust into a large circle and place on a rimmed baking sheet lined with parchment paper. Place the apple mixture on the crust. Fold over the edge of the crust so that it covers 2 to 3 inches of the apple mixture. Dot the top of the galette with chunks of butter and sprinkle with sanding sugar.
Bake for 30 to 40 minutes, until the filling is golden and bubbly.
Allow to cool slightly, then slice into wedges with a pizza cutter.