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Creamy Mushroom Asparagus Casserole with Parmesan Panko Topping

This comforting casserole features tender asparagus and earthy mushrooms bathed in a rich, creamy sauce, all topped with a golden, crispy Parmesan panko crust. It's an ideal side dish or a satisfying vegetarian main.
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Prep Time 25 minutes
Cook Time 30 minutes
Total Time 55 minutes
Servings: 6 servings
Course: Main Course, Side Dish
Cuisine: American
Calories: 350
Ingredients Equipment Method Notes

Ingredients
  

For the Mushroom & Asparagus Base
  • 1 tbsp olive oil
  • 1 lb cremini mushrooms sliced
  • 1 lb asparagus tough ends trimmed, cut into 1-inch pieces
  • 1/2 yellow onion finely diced
  • 2 cloves garlic minced
  • 1/2 tsp salt
  • 1/4 tsp black pepper
For the Creamy Sauce
  • 4 tbsp unsalted butter
  • 1/4 cup all-purpose flour
  • 2 cups whole milk warmed
  • 1/2 cup vegetable broth
  • 1/2 cup grated Parmesan cheese
  • 1/4 tsp nutmeg freshly grated (optional)
  • Salt to taste
  • Black pepper to taste
For the Topping
  • 1 cup panko breadcrumbs
  • 2 tbsp unsalted butter melted
  • 1/4 cup grated Parmesan cheese
  • 2 tbsp fresh parsley chopped (optional, for garnish)

Equipment

  • 9x13 inch baking dish
  • Large Skillet
  • Medium saucepan
  • Mixing bowls
  • Whisk

Method
 

Prepare the Vegetables
  1. Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
  2. Heat olive oil in a large skillet over medium-high heat. Add sliced mushrooms and cook, stirring occasionally, until they release their liquid and start to brown, about 5-7 minutes.
  3. Add diced yellow onion to the skillet and cook until softened, about 3-4 minutes.
  4. Stir in minced garlic and asparagus pieces. Cook for another 3-5 minutes, until asparagus is vibrant green and slightly tender-crisp. Season with 1/2 tsp salt and 1/4 tsp black pepper. Remove from heat and set aside.
Make the Creamy Sauce
  1. In a medium saucepan, melt 4 tbsp unsalted butter over medium heat.
  2. Whisk in the all-purpose flour and cook for 1-2 minutes, stirring constantly, to create a roux.
  3. Gradually whisk in the warmed whole milk and vegetable broth, ensuring no lumps form. Continue to whisk until the sauce thickens and comes to a gentle simmer, about 5-7 minutes.
  4. Remove from heat. Stir in 1/2 cup grated Parmesan cheese, nutmeg (if using), and season with salt and black pepper to taste.
Assemble and Bake
  1. Pour the creamy sauce over the cooked mushroom and asparagus mixture in the skillet. Stir gently to combine everything thoroughly.
  2. Transfer the mixture to the prepared 9x13 inch baking dish, spreading it evenly.
  3. In a small bowl, combine panko breadcrumbs, 2 tbsp melted butter, and 1/4 cup grated Parmesan cheese. Sprinkle this mixture evenly over the casserole.
  4. Bake for 25-30 minutes, or until the sauce is bubbly and the topping is golden brown and crispy.
  5. Let the casserole rest for 5-10 minutes before serving. Garnish with fresh chopped parsley if desired.

Notes

For a richer flavor, you can add a splash of dry white wine (about 1/4 cup) to the mushrooms when sautéing, letting it cook down before adding other vegetables. This casserole can be assembled ahead of time (without the breadcrumb topping) and refrigerated for up to 24 hours; add the topping just before baking. Leftovers store well in an airtight container in the refrigerator for up to 3 days.