1 large baking pumpkin (approximately 5 to 10 pounds)
1 (1-pound) loaf day-old crusty bread, such as sourdough or French baguette
1 1/2 cups (about 5 1/2 ounces) grated Gruyère cheese
2 tablespoons neutral cooking oil, such as canola
1 pound uncooked Italian sausage or bulk sausage, any casings removed
3 large shallots, thinly sliced
2 to 3 large cloves garlic, minced
1/4 cup dry white wine
2 to 3 heaping cups spinach or Swiss chard, coarsely chopped
4 large eggs
2 cups half-and-half (or 1 cup heavy cream and 1 cup whole milk)
2 teaspoons Dijon mustard
2 teaspoons kosher salt, plus more to taste
1 teaspoon fresh thyme leaves
Freshly ground black pepper
1/4 cup grated Parmesan cheese, for the top
Preheat the oven to 350°F. Line a baking sheet with parchment paper or a silicone baking mat. Place the pumpkin on a flat work surface. Using a heavy-duty knife inserted at a 45-degree angle, carefully cut out a “lid” from the top of the pumpkin. Remove any seeds and cut away any loose strings using kitchen shears. Transfer the pumpkin to the prepared baking sheet and set aside.
Combine the bread cubes and Gruyère in a large mixing bowl and set aside.
Heat the oil in a large skillet over medium to medium-high heat. Add the sausage and cook, stirring occasionally and breaking it into crumbles with a wooden spoon, until it is golden-brown and cooked through, about 8 minutes. Using a slotted spoon, transfer the sausage to the bowl with the bread and cheeses
Reduce the heat to medium and add the shallots, cooking until softened, about 5 minutes. Add the garlic and cook for 30 seconds. Increase heat to high and add the wine, using the wooden spoon to scrape up any brown bits from the bottom of the pan. Reduce the wine until it is almost evaporated. Add the spinach or chard and a generous pinch of salt; stir until wilted, 1 to 2 minutes. Add the spinach or chard to the bread mixture.
In a separate bowl, whisk the eggs, half-and-half, Dijon, 2 teaspoons salt, thyme, and pepper until combined to make the custard. Pour the custard over the bread mixture and gently toss to coat. Let sit, stirring occasionally, until absorbed, about 10 minutes.
Transfer the stuffing to the pumpkin, filling it all the way to the top. (If there is extra, you can bake it in a small dish on the side.) Fit the “lid" back onto the pumpkin and transfer to the oven.
Bake until the filling is bubbling and hot, and the flesh of the pumpkin can be pierced with a knife. This can be anywhere from 1 to 2 (or more) hours, depending on the size and type of your pumpkin. If possible, remove the cap for the last 30 to 45 minutes of baking (sprinkle with