Preheat oven to 400 degrees. Butter a 6 to 8-cup shallow gratin or baking dish.

Cut squash in half lengthwise, remove seeds and place, cut side up, in a rimmed baking pan. Season with salt and pepper, cover with aluminum foil and bake until tender but not mushy, around 1 hour. Set aside and let cool enough to handle. Leave the oven on.

While the squash is cooking, slice baguette into 1/4 to 1/2-inch pieces and toast slices until light brown. Set aside.

Heat olive oil in a medium saucepan over medium heat. Add chopped leek and 2 teaspoons water; cover and cook over medium-low heat until leek is soft, about 5 to 7 minutes.

Stir in wine. Increase heat to medium-high and boil, uncovered, for 3 minutes.

Remove from heat and stir in chicken broth, milk and sugar. Add salt and pepper to taste.

Once the squash is cool enough to handle, reheat the leek mixture.

Scoop the flesh from 1/2 of the squash into large pieces and place in the prepared baking dish, covering the bottom. Season lightly with salt and pepper.

Place approximately 1/2 of the baguette slices over the squash to cover, with space in between the slices. Cover with 1/2 of the leek mixture and 1/2 of the Gruyere cheese.

Repeat layers.

Sprinkle the top with the Parmesan cheese.

Bake for 25 to 30 minutes, or until the top is brown and bubbly

Let rest for 5 minutes, then serve.