1. Preheat the oven to 400°F (200°C). Line a sheet pan with parchment paper.

2. Toss the diced butternut squash with 1 tablespoon olive oil, salt, pepper, and 1 teaspoon thyme. Spread it out and roast for 25-30 minutes until golden and tender.

3. In a heavy skillet, heat butter and remaining olive oil over medium-low heat. Add onions and cook slowly, stirring often, for 30-40 minutes until deeply caramelized.

4. Allow the squash to cool slightly, then mash or blend until smooth.

5. In a bowl, combine mashed squash, eggs, cream, 1/2 of the goat cheese, and remaining thyme. Stir in most of the caramelized onions, saving some for topping.

6. Roll out your tart crust and place it in a tart pan. Pour in the filling and top with reserved onions and extra goat cheese.

7. Bake at 375°F (190°C) for 35-40 minutes, or until the center is set and the edges are golden.

8. Cool for 10 minutes before slicing. Serve warm or at room temperature.