For the Two-Crust Pie Dough
1. Stir the flour, sugar and salt to combine in a bowl or using a stand mixer fitted with the paddle attachment. Cut in the butter by hand with a pastry cutter or on low speed until just small pieces of butter are visible and the mixture as a whole just begins to take on a pale yellow colour (indicating that the butter has been worked in sufficiently).
2. Stir the water and lemon juice together and add this to the dough all at once, mixing until the dough just comes together. Shape the dough into 2 discs, wrap and chill for at least 2 hours before rolling. Alternatively, the dough can be frozen for up to 3 months and thawed in the fridge before rolling.
3. Shape into 2 logs and chill.
For the Apple Cinnamon Galettes
1. Preheat the oven to 375 F and line 2 baking trays with parchment paper. Pull the pie dough from the fridge 20 minutes before rolling.
2. Slice each log into 3 pieces and roll each piece out on a lightly floured work surface to just under ¼-inch thickness and 8-inches across. Place 3 onto each baking tray and chill while preparing the filling.
3. Stir the sour cream, 2 Tbsp of brown sugar and vanilla together. In another bowl, toss the apples, remaining ½ cup of brown sugar and cinnamon together.
4. Spoon the sour cream into the centre of each rolled piece of dough and top with the sliced apples. Place a teaspoon of butter on the top of each tart. Fold the dough over the apples, making 5 or 6 creases overlapping each other so that the apples are almost fully covered. Brush the pastry with the eggwash and sprinkle generously with granulated sugar.
5. Bake the galettes for about 25 minutes, until the pastry is a rich golden brown colour. Let the galettes cool for at least 20 minutes before serving warm, or cool completely and serve at room temperature.
The galettes should be served warm or at room temperature, but can be stored chilled for up to 3 days.