01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large bowl, toss the butternut squash, apples, and red onion with olive oil, thyme, salt, and pepper. Spread on the baking sheet and roast for 20–25 minutes, until tender and lightly caramelized. Let cool slightly.
03 - While the vegetables roast, mix flour and salt in a bowl. Use a pastry cutter or fingers to cut in the cold butter until the mixture resembles coarse crumbs. Add ice water, 1 tablespoon at a time, mixing just until the dough comes together. Form into a disc, wrap in plastic, and chill for 20 minutes.
04 - On a lightly floured surface, roll out the dough to a 12-inch circle. Transfer to a parchment-lined baking sheet.
05 - Arrange the roasted squash, apples, and onion in the center, leaving a 2-inch border. Sprinkle with goat cheese and drizzle with honey if using.
06 - Fold the dough edges over the filling, pleating as you go, to form a rustic galette. Brush the crust with beaten egg and sprinkle with coarse sugar if desired.
07 - Bake for 25–30 minutes, until the crust is golden brown. Let cool slightly before slicing and serving.