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 - In a bowl, mix flour and salt. 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.