Stuffed Butternut Squash with Mushrooms and Spinach

Stuffed Butternut Squash

Roasted butternut squash halves make sturdy, skin-on boats for browned mushrooms, spinach, and patches of melted cheese. Leave a broad border of orange squash around the filling so each serving holds together and tastes like squash, not just stuffing.

Roast the halves until the thick necks are fork-tender while you cook the filling in a skillet. A shallow channel pressed into the tender neck makes room for the mushrooms without hollowing out the squash. Serve one half as a vegetarian main or a substantial side.

Ingredients for Stuffed Butternut Squash

• 2 medium butternut squash, about 1½–2 pounds each
• 2 tablespoons olive oil, divided
• 1 teaspoon kosher salt, divided, plus more to taste
• ½ teaspoon freshly ground black pepper, divided
• 12 ounces sliced cremini mushrooms (340g)
• 1 small yellow onion, finely diced (about 110g)
• 2 garlic cloves, minced
• 5 ounces baby spinach (about 140g)
• 1 teaspoon fresh thyme leaves
• ¾ cup shredded low-moisture mozzarella (about 85g)
• ¼ cup finely grated Parmesan (about 25g)
• 2 tablespoons chopped fresh flat-leaf parsley

Yield: 4 servings, one squash half each. Time: About 20 minutes prep and 45–65 minutes cooking, or 65–85 minutes total. Make the filling while the squash roasts.

How to Make Stuffed Butternut Squash

1. Prepare the squash: Preheat the oven to 400°F (205°C) with a rack near the center. Trim a small amount from each end of each squash. Steady the squash on a sturdy cutting board and carefully cut them in half lengthwise with a sharp chef’s knife. Scoop out the seeds, leaving the skin on. Rub the cut surfaces with 1 tablespoon olive oil and season with ½ teaspoon salt and ¼ teaspoon pepper.
2. Roast until tender: Place the halves cut-side down, with space between them, on a large rimmed baking sheet. Roast uncovered, starting to check after 35 minutes. Expect about 40–55 minutes, but continue until a fork easily pierces the thick flesh at the neck. Browning alone does not mean the squash is ready to stuff.
3. Brown the mushrooms: While the squash roasts, heat the remaining tablespoon of oil in a large skillet over medium-high heat. Add the mushrooms and cook for about 8–10 minutes, stirring occasionally and allowing the slices time to brown. Cook until their released liquid has evaporated and none pools in the skillet.
4. Finish the filling: Reduce the heat to medium. Add the onion and cook until softened, then stir in the garlic and thyme. Add the spinach in batches and cook until wilted. Continue cooking uncovered if liquid collects in the skillet. Season with the remaining ½ teaspoon salt and ¼ teaspoon pepper; taste and adjust the salt if needed.
5. Shape and fill: Let the roasted squash stand for a few minutes, then carefully turn the halves cut-side up. Gently press down the tender flesh along each narrow neck with a spoon to form a shallow channel. Scoop out only a little flesh if necessary, keeping the halves intact. Divide the filling among them, leaving a broad orange border visible.
6. Melt the cheese: Scatter the mozzarella and Parmesan in loose patches over the filling, leaving some mushrooms and greens visible. Return the sheet to the 400°F oven for about 5–8 minutes. Start checking after 5 minutes; the filling should be hot and the cheese melted and lightly golden in places. Sprinkle with parsley before serving.

Check the Thick Neck Before Stuffing

The flesh around the seed cavity can soften before the thick neck does. Test the neck with a fork: it should slide in easily. Larger or thicker halves may need more than 55 minutes. Finish roasting them before adding the filling, since the short cheese-melting bake will not cook a firm neck through.

Keep the Filling in the Squash

The bulbous end has a natural cavity, but the neck has little room for filling. Pressing its cooked flesh into a shallow channel gives the mushrooms a place to sit without turning the squash into a thin shell. Keep the filling below the edges so it does not slip off.

Keep the Mushroom Filling from Getting Watery

Use a roomy skillet so mushroom moisture can evaporate and the slices can brown rather than steam. Add the spinach only after the mushroom liquid has cooked off, then cook away any moisture the greens release before stuffing the squash. Chopped kale can replace the spinach, but cook it until tender and dry.

Serving, Make-Ahead, and Storage

Serve one half with a simple salad for a vegetarian dinner. For a holiday meal, serve smaller portions alongside prime rib roast.

To make the dish ahead, roast the squash and prepare the filling separately up to one day in advance. Refrigerate both, then assemble and heat until hot throughout and the cheese melts. Cold components may need longer than the brief final bake for freshly cooked squash.

Refrigerate cooled leftovers covered or in an airtight container for up to 3 days. Reheat in the oven until hot throughout; the time depends on the size and temperature of the portions.

Nutrition

Approximate nutrition per serving (one stuffed squash half): 340 calories, 15g protein, 14g fat, and 46g carbohydrates. Approximate values per 100g of finished dish: 75 calories, 3g protein, 3g fat, and 10g carbohydrates. Values vary with squash size, edible yield, and cheese brands.