Preheat the oven to 400°F (200°C). Toss the cubed butternut squash with olive oil, salt, and pepper. Spread on a baking sheet and roast for 25–30 minutes until golden and tender.

While the squash roasts, caramelize the onions. Heat olive oil in a pan over medium-low heat. Add sliced onions and cook, stirring often, for 30–40 minutes until golden brown and soft.

Roll out the puff pastry on a parchment-lined baking sheet. Score a 1-inch border around the edge and prick the center with a fork. Pre-bake for 10 minutes.

Spread the caramelized onions over the pre-baked puff pastry. Top with roasted squash, crumbled goat cheese, and sprinkle with thyme.

Brush edges with egg wash if using. Bake for 15–20 minutes until the pastry is golden and crisp.

Cool slightly before slicing. Serve warm or at room temperature.