Preheat the oven to 400°F (200°C). Peel and dice the butternut squash, and thinly slice the onions.

Toss the diced squash with olive oil, salt, and black pepper. Spread in a single layer on a baking sheet and roast for 25-30 minutes until tender and golden.

Heat a tablespoon of olive oil in a skillet over medium heat. Add the sliced onions and cook for about 20 minutes until golden brown.

Roll out the puff pastry to fit your tart pan and place it inside. Prick the bottom to prevent bubbling.

Spread the caramelized onions on the pastry, add the roasted butternut squash, crumbled goat cheese, drizzle heavy cream, and sprinkle thyme and red pepper flakes.

Bake in the oven for 25-30 minutes until the pastry is golden brown and flaky.

Let cool for 10 minutes on a wire rack before serving warm.