Preheat your oven to 400°F (200°C).

Peel and dice the butternut squash into small cubes, then toss with olive oil, salt, and black pepper. Roast in the oven for 25-30 minutes until fork-tender.

Heat olive oil in a skillet, add sliced onions with a pinch of salt, and cook for about 20 minutes until caramelized.

Roll out the puff pastry to fit your tart pan, about 1/8-inch thick, and press into the pan. Prick the bottom with a fork.

Spread caramelized onions over the pastry base, layer roasted butternut squash on top, crumble goat cheese, and drizzle with heavy cream. Sprinkle with thyme.

Bake in the oven for 25-30 minutes until the pastry is golden brown and cheese is slightly melted. Brush edges with a beaten egg during the last 5 minutes of baking.

Allow tart to cool for about 10 minutes before slicing. Serve warm or at room temperature.