Spinach and Mushroom Casserole
This Spinach and Mushroom Casserole is creamy, rich, and packed with earthy mushrooms and tender spinach, all topped with a golden, crunchy panko crust. Gruyere cheese adds a nutty depth that makes every bite feel a little luxurious, while the make-ahead friendly preparation makes it perfect for holiday gatherings. It looks impressive but comes together faster than you'd think.
Equipment
- Large skillet 12-inch works great
- 9x13-inch baking dish
- Large pot for blanching spinach
- Cutting board and sharp knife
- Wooden spoon for stirring
- Measuring cups and spoons
- Colander for draining spinach
- Cheese grater
- Small mixing bowl
Ingredients
- 2 pounds fresh spinach 900g, washed
- 1 pound mushrooms 450g, sliced
- 4 tablespoons butter 56g, divided
- 1 onion diced
- 4 cloves garlic minced
- 3 tablespoons all-purpose flour
- 2 cups heavy cream 480ml
- 1 cup vegetable broth 240ml
- 1 1/2 cups Gruyere cheese shredded, about 150g
- 1/2 cup Parmesan cheese grated, about 50g
- 1 teaspoon salt
- 1/2 teaspoon black pepper
- 1/4 teaspoon nutmeg
- 1/2 cup panko breadcrumbs
- 2 tablespoons olive oil
Instructions
- Bring a large pot of salted water to a rolling boil. Blanch the fresh spinach in batches for exactly 1 minute until wilted and bright green, then transfer to a colander and run cold water over it to stop the cooking.
- Once cooled, squeeze handfuls of spinach firmly to remove as much water as possible, then roughly chop and set aside.
- Heat 2 tablespoons of butter in a large skillet over medium-high heat until foaming. Add the sliced mushrooms in a single layer and cook undisturbed for 3-4 minutes to brown, then stir and cook another 3-4 minutes until moisture evaporates. Season with salt and pepper and transfer to a plate.
- In the same skillet, add the remaining 2 tablespoons of butter over medium heat. Cook the diced onion for 5-6 minutes until softened and translucent, then add the minced garlic and cook for 1 minute until fragrant.
- Sprinkle the flour over the onion and garlic and stir constantly for 2 minutes to create a roux. Slowly pour in the heavy cream while whisking continuously, then add the vegetable broth and whisk until smooth.
- Bring the sauce to a gentle simmer and cook for 3-4 minutes until thickened enough to coat the back of a spoon. Stir in the Gruyere and Parmesan until melted, then season with salt, pepper, and nutmeg.
- Return the cooked mushrooms to the skillet with the cream sauce, add the chopped squeezed spinach, and stir gently but thoroughly until evenly distributed. Taste and adjust seasoning.
- Preheat the oven to 375°F (190°C) and lightly grease a 9x13-inch baking dish. Pour the spinach and mushroom mixture into the dish and spread it evenly with a spatula.
- Mix the panko breadcrumbs with the olive oil in a small bowl until all crumbs are coated, then sprinkle evenly over the top of the casserole, covering the entire surface.
- Bake on the center rack for 25-30 minutes until the top is golden brown and the edges are bubbling. Tent loosely with foil if the breadcrumbs brown too quickly.
- Remove from the oven and let rest for 5-10 minutes before serving to allow the sauce to set slightly.
Notes
- Squeeze the spinach dry thoroughly — this is the most important step, as excess water will make the casserole runny and dilute the flavors.
- Don't crowd the mushrooms in the pan; give them space so they brown instead of steam.
- Use freshly grated cheese — pre-shredded cheese contains anti-caking agents that prevent smooth melting.
- Toss the panko with olive oil before sprinkling to create a crunchier, more flavorful topping that stays crispy.
- Let the casserole rest 5-10 minutes after baking so it sets and serves cleanly.
- Season in layers — add salt and pepper at each stage (mushrooms, sauce, final mixture) for deeper flavor.
- Make ahead: assemble completely, cover tightly, and refrigerate up to 24 hours. Add 10 minutes to baking time if starting cold.
- Frozen spinach substitution: use two 10-ounce packages of frozen chopped spinach, thawed and squeezed very dry; skip the blanching step.
- Gruyere substitute: Swiss cheese is closest, but fontina, Emmental, or sharp white cheddar also work well.
- Storage: refrigerate covered for up to 4 days, or freeze individual portions for up to 3 months. Reheat covered with foil at 350°F for 20-25 minutes, removing foil for the last 5 minutes to re-crisp the topping.
Nutrition
Serving: 1ServingCalories: 385kcalCarbohydrates: 12gProtein: 14gFat: 32gSaturated Fat: 18gCholesterol: 95mgSodium: 520mgFiber: 2gSugar: 3gVitamin A: 85IUVitamin C: 20mgCalcium: 35mgIron: 15mg
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