Crispy-Topped Homestyle Tuna Casserole

Preheat the oven to 400 degrees Fahrenheit. Lightly grease a 9-by-13-inch baking dish with butter or cooking spray.

Bring a large pot of salted water to a boil. Cook the egg noodles for 2 minutes less than the package directions indicate (they will finish cooking in the oven). Drain, toss with a small drizzle of olive oil to prevent sticking, and set aside.

While the noodles cook, melt 3 tablespoons of the butter in a large saucepan over medium heat. Add the sliced mushrooms and cook for 5 to 6 minutes, stirring occasionally, until they release their liquid and turn golden brown.

Add the diced onion and celery. Cook for 3 to 4 minutes until the vegetables soften and the onion turns translucent. Add the garlic and cook for 30 seconds until fragrant.

Sprinkle the flour over the vegetables and stir constantly for 2 minutes to cook out the raw flour taste and form a smooth roux.

Gradually pour in the warmed milk, about 1/2 cup at a time, whisking vigorously after each addition to prevent lumps. Add the chicken broth and continue whisking until the sauce is smooth.

Bring the sauce to a gentle simmer and cook for 3 to 4 minutes, stirring frequently, until it thickens enough to coat the back of a spoon. Remove from heat.

Stir in the Dijon mustard, salt, pepper, nutmeg, and 3/4 cup of the shredded cheddar until the cheese melts completely into the sauce. Gently fold in the drained tuna and frozen peas.

Add the par-cooked egg noodles to the sauce and fold everything together until the noodles are evenly coated. Pour the mixture into the prepared baking dish and spread it into an even layer.

In a small bowl, combine the Panko breadcrumbs, the remaining 1/4 cup of cheddar cheese, the remaining 1 tablespoon of butter (melted), and the olive oil. Toss until the breadcrumbs are evenly coated and scatter the mixture over the top of the casserole.

Bake uncovered for 20 to 25 minutes, until the filling is bubbling around the edges and the topping is deeply golden brown and crisp.

Let the casserole rest for 5 minutes before serving. Garnish with chopped fresh parsley.