What’s the secret to perfectly roasted mushrooms? It’s a simple technique that transforms humble fungi into a rich, savory side dish. You’ll love how these mushrooms caramelize in the oven, becoming tender and bursting with umami flavor. Perfect for weeknight dinners or holiday feasts, this recipe is a game-changer. ### Why You’ll Love This Recipe This recipe turns ordinary mushrooms into something extraordinary. The high-heat roasting method deepens their natural flavors, resulting in a dish that’s both elegant and easy. It’s a versatile side that pairs well with almost any main course. ### Benefits – **Effortless Elegance**: Requires just a few ingredients and minimal prep time. – **Weeknight Winner**: Ready in under 30 minutes, perfect for busy evenings. – **Crowd-Pleaser**: Even mushroom skeptics will be won over by the rich, savory results. ### Ingredients – 1 pound portobello mushrooms, stems removed and caps sliced ½-inch thick – 2 tablespoons olive oil – ½ teaspoon kosher salt – ¼ teaspoon black pepper – 3 tablespoons unsalted butter – 1 medium yellow onion, thinly sliced – 2 cloves garlic, minced – 3 tablespoons all-purpose flour – 1½ cups whole milk – ½ cup heavy cream – 1 teaspoon fresh thyme leaves – ¼ teaspoon ground nutmeg – 1 cup shredded Gruyère cheese, divided – ½ cup grated Parmesan cheese ### Instructions 1. **Prep the Mushrooms**: Preheat your oven to 375°F. Toss the mushroom slices with olive oil, salt, and pepper. Arrange them in a single layer on a baking sheet. 2. **Roast**: Roast for 15 minutes, or until the mushrooms have released their liquid and are tender. Set aside. 3. **Sauté Aromatics**: Melt the butter in a large skillet over medium heat. Add the onion and cook until softened and translucent, about 8-10 minutes. Stir in the garlic and cook for 1 minute until fragrant. 4. **Make the Sauce**: Sprinkle the flour over the onions and garlic, stirring to form a paste. Gradually whisk in the milk and heavy cream until smooth. Bring to a simmer, stirring constantly, until the sauce thickens enough to coat the back of a spoon, about 3-5 minutes. 5. **Combine**: Remove from heat and stir in the thyme, nutmeg, ¾ cup of the Gruyère cheese, and all of the Parmesan cheese until melted and smooth. Gently fold in the roasted mushroom slices. 6. **Bake**: Transfer the mixture to a 2-quart baking dish and sprinkle the remaining ¼ cup of Gruyère cheese evenly over the top. Bake at 350°F for 20-25 minutes, or until the cheese is golden brown and the sauce is bubbly around the edges. 7. **Rest and Serve**: Let the dish rest for 5-10 minutes before serving to allow the sauce to set. ### Notes – **Storage**: Keep leftovers in an airtight container in the refrigerator for up to 3 days. – **Reheating**: Gently reheat in the oven or on the stovetop to maintain the best texture. – **Freezing**: This dish can be frozen for up to 2 months. Thaw overnight in the refrigerator before reheating. ### Nutrition – **Calories**: 320kcal – **Carbohydrates**: 12g – **Protein**: 15g – **Fat**: 24g – **Saturated Fat**: 13g – **Cholesterol**: 70mg – **Sodium**: 520mg – **Potassium**: 480mg – **Fiber**: 2g – **Sugar**: 6g – **Vitamin A**: 750IU – **Vitamin C**: 2mg – **Calcium**: 380mg – **Iron**: 1mg ### Keywords creamy mushroom bake, Gruyère mushroom casserole, easy mushroom recipe, roasted portobello mushrooms, holiday side dish — **Q: Can I use different types of mushrooms?** **A:** Absolutely! Cremini or white mushrooms work well too. Adjust slicing as needed for uniform cooking. **Q: How can I make this dish vegetarian?** **A:** It already is! Just double-check your cheese labels to ensure they’re vegetarian-friendly. **Q: Can I prepare this ahead of time?** **A:** Yes, assemble the dish up to a day in advance, cover, and refrigerate. Add a few extra minutes to the baking time if starting from cold. — *Enjoy this comforting, creamy mushroom bake—it’s sure to become a new favorite at your table!*