Add flour, sugar, salt, and butter to a food processor and pulse until the butter is pea-sized. Continue pulsing while drizzling in the cold water 1 tablespoon at a time. Stop adding water as soon as the pie crust forms a ball.

Place the ball on a floured surface and work the ball into a disk. Wrap in plastic wrap and chill in the refrigerator for at least 2 hours.

Combine melted butter, brown sugar, lemon juice, cinnamon, salt, and corn starch in a medium bowl. Whisk to combine.

Preheat the oven to 400 degrees and set aside a large baking sheet.

Roll out the chilled pie crust on a large piece of parchment paper using a rolling pin. Use your hands to patch up any cracks. The pie crust should be a large rough circle and ½ inch in thickness when done.

Brush the pie crust with egg white. The prevents a soggy bottom.

Arrange the sliced apples in the center of the pie crust.

Gently fold the sides of the pie crust into the center. It is ok if this doesn’t look perfect.

Once all sides are folded in, brush the edges with egg and sprinkle with brown sugar.

Pour the brown sugar butter mixture over the top of the apples. Do not pour on the sides of the pie crust. Just pour the sauce in the center.

Lift the parchment paper that holds the galette and place it on the baking sheet.

Bake in the oven for 45 minutes. The crust should be golden brown.

Let the galette cool completely either on a wire rack or on the baking sheet.