Step 1: In a large bowl, whisk together the all-purpose flour, granulated sugar, and salt. Add the cold cubed butter and use a pastry cutter or your fingers to work the butter into the flour until it resembles coarse crumbs with some pea-sized pieces.
Step 2: Gradually add ice water, one tablespoon at a time, mixing until the dough just begins to hold together. Shape the dough into a disk, wrap in plastic, and refrigerate for at least 30 minutes.
Step 3: Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Step 4: In a medium bowl, toss the sliced nectarines with brown sugar, cinnamon, cardamom, and lemon juice until evenly coated.
Step 5: On a lightly floured surface, roll the chilled dough into a 12-inch circle. Transfer the dough to the prepared baking sheet.
Step 6: Sprinkle the almond flour over the center of the dough, leaving a 2-inch border around the edges.
Step 7: Arrange the nectarine slices over the almond flour in a decorative pattern or a simple pile.
Step 8: Fold the edges of the dough up and over the nectarines, pleating as you go. Brush the crust with the beaten egg and sprinkle with turbinado sugar if desired.
Step 9: Bake for 30-35 minutes, or until the crust is golden brown and the fruit filling is bubbly. Let cool for at least 15 minutes before slicing.