1. Preheat oven to 400°F. Toss the butternut squash cubes with olive oil, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Spread on a baking sheet and roast for 20-25 minutes, until tender.

2. In a large skillet, melt the butter over medium heat. Add the sliced onions and cook for 20-25 minutes, stirring occasionally, until caramelized and golden brown. Stir in the brown sugar and remaining 1/2 teaspoon salt and 1/4 teaspoon black pepper. Set aside.

3. Roll out the pie crust and press it into a 9-inch tart pan with a removable bottom. Prick the bottom with a fork.

4. In a medium bowl, whisk together the eggs and heavy cream. Pour the mixture into the tart shell.

5. Arrange the roasted butternut squash cubes over the egg mixture, then top with the caramelized onions.

6. Bake for 35-40 minutes, until the center is set. Sprinkle the Parmesan cheese over the top.

7. Allow the tart to cool for 10 minutes before slicing and serving.