Add flour and salt to the bowl of a food processor. Pulse a few times to combine.
1 ½ cups all-purpose flour, ½ teaspoon kosher salt
Add cubed butter. Pulse again until it forms a crumb.
10 tablespoons cold unsalted butter
Pour in 3 tablespoons cold water and apple cider vinegar. Pulse just until it forms a thick dough.
1 teaspoon apple cider vinegar
Lightly flour a clean surface and a rolling pin. Form the dough into a disc and roll the dough into a circle over the floured surface until it’s about ⅛ of an inch thick and about 12 inches wide. (The thinner, the better.)
Carefully use the rolling pin to help transfer the dough to a parchment-lined baking sheet.
Place baking sheet in the fridge, and let dough chill for at least 1 hour.
Preheat oven to 375 degrees F.
Filling
Place sliced apples in a large bowl. Add brown sugar, lemon juice, vanilla, and cinnamon. Gently stir to coat the apples.
3 baking apples, ¼ cup light brown sugar, 2 teaspoons fresh lemon juice, ½ teaspoon vanilla extract, ½ teaspoon ground cinnamon
Remove dough from the fridge. Starting in the center, place apples in the center of the dough in concentric circles, leaving about 2 inches around the edge of the dough.
Fold dough around the edge over the top of the apples, overlapping where necessary.
Finish
In a small bowl, whisk to combine egg and ½ tablespoon water. Brush on top of the dough. Sprinkle raw sugar on top of the egg. Place remaining 2 tablespoons of cubed butter evenly on top of the apples.
1 large egg, ½ tablespoon turbinado or raw sugar
Bake galette for 35-40 minutes, or until apples are tender and the crust is lightly golden brown.
Notes
Flour: To properly measure the flour, weigh it or sift to break the flour up, lightly spoon into a measuring cup, and level. Avoid packing the flour.
Salt: Sea salt make a good substitute. If using table salt, use half the amount of salt.
Butter: If using salted butter, omit the salt.
Lemon juice: It's important to use fresh lemon juice because bottled lemon juice can have an off taste.