Preheat your oven to 425°F (220°C). Cut the butternut squash into uniform cubes and toss them in a bowl with olive oil, cinnamon, garlic powder, onion powder, and a pinch of cayenne. Spread the seasoned squash on a baking sheet in a single layer. Roast for 15-20 minutes, or until the squash is tender and lightly browned, stirring halfway through for even cooking.

While the squash is roasting, heat a tablespoon of olive oil in a skillet over medium heat. Add sliced red onions and sauté for about 3-5 minutes, or until they become translucent and fragrant. Remove from heat and set aside to cool slightly.

Once the squash is done roasting, lower the oven temperature to 350°F (175°C). Roll out your pie dough into a 12-14 inch circle, about ⅛ inch thick. Transfer the rolled dough onto a piece of parchment paper.

Spread a layer of Boursin cheese over the center of the dough, leaving a 1-inch border around the edges. Layer the roasted butternut squash and sautéed onions evenly atop the cheese. Sprinkle crispy sage leaves on top.

Gently fold the edges of the dough over the filling to create a rustic border. Brush the exposed dough with heavy cream and sprinkle grated Parmesan cheese and black pepper over the top.

Bake for 45-50 minutes, or until the crust is golden brown and flaky. Allow the galette to cool for 5-10 minutes before slicing.