Baked Cheesy Mushroom Casserole: A Comforting Delight

Making the Cheese Sauce

In a separate saucepan, melt the remaining 3 tablespoons butter over medium heat. Sprinkle the flour over the butter and whisk continuously for 2 minutes to form a blonde roux—this eliminates any raw flour taste. Slowly pour the warm milk while whisking, allowing the mixture to thicken without lumps. Once the sauce coats the back of a spoon, stir in Dijon mustard, smoked paprika, and half of the thyme. Reduce heat to low and fold in the cheddar and mozzarella until they melt into a smooth, glossy sauce.

Assembling the Casserole

Preheat your oven to 375°F (190°C). In a greased 9‑inch baking dish, spread the sautéed mushrooms evenly. Pour the cheese sauce over the mushrooms, using a spatula to ensure full coverage. Sprinkle the remaining thyme and a pinch of salt and pepper on top for extra flavor.

Creating the Crunchy Topping

1. Combine breadcrumbs and butter. In a small bowl, mix the panko breadcrumbs with 2 tablespoons melted butter until every crumb is lightly coated. The butter will toast the crumbs, giving them a buttery crunch.
2. Apply the topping. Evenly scatter the buttered breadcrumbs over the cheese‑laden casserole. Press gently with the back of a spoon to create a uniform layer that will brown evenly.
3. Bake to perfection. Place the dish in the preheated oven and bake for 20‑25 minutes, or until the topping turns golden brown and the sauce bubbles at the edges. A visual cue of a deep amber crust signals it’s ready.
4. Rest before serving. Remove the casserole from the oven and let it sit for 5 minutes. This short rest allows the sauce to set, making it easier to slice and serving each portion with a perfect balance of sauce and crunch.