📝 About This Recipe
This comforting casserole is a celebration of forest-floor flavors, marrying the deep umami of sautéed cremini mushrooms with the vibrant, mineral notes of fresh baby spinach. Bathed in a velvety, nutmeg-scented Mornay sauce and topped with a golden, buttery panko crust, it offers a sophisticated twist on classic vegetable bakes. Perfect as a decadent holiday side or a hearty vegetarian main, this dish is the ultimate culinary hug in a baking dish.
🥗 Ingredients
The Vegetable Base
- 1.5 pounds Cremini Mushrooms (cleaned and thickly sliced)
- 16 ounces Fresh Baby Spinach (washed and dried thoroughly)
- 1 Yellow Onion (finely diced)
- 4 pieces Garlic Cloves (minced)
- 2 tablespoons Unsalted Butter (for sautéing)
- 1 tablespoon Fresh Thyme (leaves stripped from stems)
The Cream Sauce
- 4 tablespoons Unsalted Butter
- 1/4 cup All-Purpose Flour
- 2 cups Whole Milk (warmed slightly)
- 1.5 cups Gruyère Cheese (freshly shredded)
- 1/4 teaspoon Nutmeg (freshly grated if possible)
- 1 teaspoon Kosher Salt (adjust to taste)
- 1/2 teaspoon Black Pepper (freshly cracked)
The Crunchy Topping
- 3/4 cup Panko Breadcrumbs
- 1/2 cup Parmesan Cheese (finely grated)
- 2 tablespoons Unsalted Butter (melted)
👨🍳 Instructions
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1
Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish or a 2.5-quart ceramic casserole dish with butter.
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2
In a large skillet over medium-high heat, melt 2 tablespoons of butter. Add the sliced mushrooms in a single layer and cook undisturbed for 4-5 minutes until deep golden brown.
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3
Stir the mushrooms and add the diced onions. Sauté for another 5 minutes until the onions are translucent and the mushrooms have released their moisture.
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4
Stir in the minced garlic and fresh thyme. Cook for 1 minute until fragrant, then add the baby spinach in batches, tossing until just wilted. Remove from heat and drain any excess liquid from the pan.
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5
In a medium saucepan over medium heat, melt the 4 tablespoons of butter for the sauce. Whisk in the flour and cook for 2 minutes to create a light roux, ensuring it doesn't brown.
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6
Slowly drizzle in the warm milk while whisking constantly to prevent lumps. Continue cooking and whisking until the sauce thickens enough to coat the back of a spoon (about 5-7 minutes).
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7
Remove the sauce from heat. Stir in 1 cup of the Gruyère cheese, salt, pepper, and nutmeg until the cheese is completely melted and the sauce is glossy.
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8
Combine the sautéed vegetable mixture with the cheese sauce in a large mixing bowl, tossing gently to ensure every mushroom and leaf is coated.
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9
Transfer the mixture into your prepared baking dish, spreading it out into an even layer.
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10
In a small bowl, mix the panko breadcrumbs, grated Parmesan, and 2 tablespoons of melted butter until the crumbs are evenly moistened.
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11
Sprinkle the remaining 1/2 cup of Gruyère over the casserole, followed by the buttery panko-Parmesan mixture.
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12
Bake in the center of the oven for 20-25 minutes, or until the sauce is bubbling around the edges and the topping is a beautiful golden brown.
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13
Remove from the oven and let rest for 5-10 minutes before serving. This allows the sauce to set slightly for the perfect texture.
💡 Chef's Tips
Don't crowd the mushrooms; if your pan is small, sauté them in two batches to ensure they brown rather than steam. Always squeeze or drain the cooked spinach-mushroom mixture well to prevent a watery casserole. Use a block of Gruyère and grate it yourself; pre-shredded cheeses are coated in potato starch which can make the sauce grainy. For an extra layer of flavor, add a splash of dry white wine to the mushrooms after they've browned and let it reduce completely. If the topping browns too quickly, tent the dish loosely with foil for the last 10 minutes of baking.
🍽️ Serving Suggestions
Serve alongside a roasted herb-crusted chicken or a juicy ribeye steak. Pair with a crisp, chilled Chardonnay or a light Pinot Noir to complement the earthy mushrooms. A side of crusty sourdough bread is essential for mopping up the extra cream sauce. Accompany with a bright arugula salad dressed in a lemon vinaigrette to cut through the richness. This dish also makes a fantastic base for a brunch; top a scoop with a poached egg.