Methods

1. To make the dough, combine the flour, granulated white sugar, and 1 teaspoon Diamond Crystal or ½ teaspoon fine sea salt in a medium bowl. Cut 8 tablespoons of cold butter into cubes and add it to the flour mixture. Using your fingers, rub the cubes of butter into the flour until the butter is the size of chickpeas. 
2. Add 4 tablespoons ice water to the flour-butter mixture and gently stir until a very shaggy dough starts to form. Squeeze the dough together to form a ball. (If the dough seems dry, add 1 tablespoon of water at a time until it comes together.) 
3. Place the dough ball on a piece of parchment paper or plastic wrap and then place another piece of parchment paper or plastic wrap on top and roll the dough into a 10-inch round. Remove the top piece of parchment and fold the dough in half lengthwise and then in half again crosswise (this is creating lots of flaky layers!). Form the dough back into a disk, wrap completely, and chill for 1 hour.
4. About 15 minutes before rolling out your galette, melt the remaining 3 tablespoons butter in a small saucepan over medium heat. Whisk in the jaggery, garam masala, orange zest, and remaining ½ teaspoon Diamond Crystal or ¼ teaspoon fine sea salt into the melted butter and continue to heat until the jaggery starts to melt, about 30 seconds to 1 minute. Turn off the heat, add the orange juice and cornstarch, and whisk until smooth. Set aside.
5. To prepare the apples, cut one cheek of the apple off away from the core. Then cut the cheek on the opposite side, followed by the two smaller cheeks, leaving the core. Thinly slice each apple cheek and gently press down to fan them just slightly. Repeat with the remaining apples and set aside.
6. To roll and assemble the galette, place the chilled dough on a lightly floured surface, roll into a 15-inch round, and transfer to a parchment-lined baking sheet. Arrange the apple fans in the center of the round, leaving about a 2-inch border all the way around. Drizzle the reserved spiced butter mixture over the apples, then fold the dough border up over the apples, pleating as needed. Transfer the pan to the freezer and chill for 15 to 20 minutes.
7. While the galette is chilling, preheat the oven to 375°F.
8. Remove the chilled galette from the freezer, brush the dough with egg wash, and sprinkle with demerara sugar, if using (alternatively, you can sprinkle with granulated white sugar). Bake until the crust is deep golden and apples are cooked through, about 42 to 48 minutes. Serve warm or at room temperature with a dollop of lightly sweetened whipped cream or vanilla ice cream.