01 - In a large bowl, whisk together the flour and salt. Add cold butter and cut in with a pastry blender or fingertips until coarse crumbs form. Gradually add ice water, one tablespoon at a time, mixing just until dough starts to come together. Shape into a disc, wrap in plastic, and refrigerate for at least 30 minutes.
02 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
03 - In a large bowl, toss diced butternut squash and sliced onion with olive oil, thyme, nutmeg, salt, and pepper. Spread evenly on the prepared baking sheet and roast for 20 minutes.
04 - Remove baking sheet from oven, add apple slices, gently toss, and return to oven for 15 more minutes until squash is tender and apples are slightly softened. Let cool slightly.
05 - On a lightly floured surface, roll chilled dough into a 12-inch circle. Transfer to the parchment-lined baking sheet.
06 - Spread roasted squash, onion, and apple mixture evenly over the dough, leaving a 2-inch border. Sprinkle crumbled goat cheese and parsley over filling.
07 - Fold dough edges up and over the filling, pleating as needed. Brush the crust with the beaten egg and sprinkle with coarse sea salt if desired.
08 - Bake for 30 to 35 minutes until the crust is golden and cooked through. Let cool slightly before slicing and serving.