Prepare the Dough: In a large bowl, whisk together 1 ½ cups flour and ½ teaspoon salt. Add ½ cup cold, cubed butter and cut it into the flour using a pastry blender or fingertips until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining. Gradually add ½ cup ice water, one tablespoon at a time, mixing until the dough just comes together. Form into a disk, wrap in plastic, and refrigerate for at least 30 minutes.

Prepare the Filling: While the dough chills, combine 2 medium apples (thinly sliced), 1 cup cranberries, ¼ cup granulated sugar, 1 tablespoon all-purpose flour, ½ teaspoon cinnamon, and 1 tablespoon lemon juice in a large bowl. Toss gently until evenly coated.

Roll Out the Dough: Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper. On a lightly floured surface, roll out the chilled dough into a rough 12-14 inch circle.

Assemble the Galette: Transfer the dough to the prepared baking sheet. Arrange the fruit filling in the center, leaving a 2-inch border. Fold the edges of the dough over the fruit, pleating to form a rustic crust.

Egg Wash and Sugar: Whisk 1 egg yolk and 1 tablespoon water for an egg wash. Brush over the folded crust. Sprinkle 1 tablespoon turbinado sugar generously over the crust.

Bake the Galette: Bake for 35-45 minutes, or until the crust is golden brown and the fruit filling is bubbly and tender. Loosely cover edges with foil if browning too quickly.

Cool and Serve: Remove from oven and let cool on the baking sheet for 15-20 minutes before slicing. Serve warm, optionally with vanilla ice cream or whipped cream.