Yield: 6 to 8 servings.
1 (8-ounce) package wide egg noodles, cooked al dente per instructions
7 tablespoons unsalted butter, divided
½ medium onion, chopped
2 stalks celery, diced
¼ cup all-purpose flour
3 cups whole milk
2 large eggs, beaten
1 teaspoon salt
1 teaspoon freshly cracked black pepper
½ teaspoon garlic powder
2 (5-ounce) cans tuna, drained and flaked
1 can diced water chestnuts, drained
½ cup fresh parsley, coarsely chopped
1 cup plain bread crumbs
1 cup shredded Cheddar cheese
Preheat oven to 350°. Prepare a 9 x 12-inch baking dish with cooking spray. In a medium skillet, melt 1 tablespoon butter over medium-low heat. Stir in the onion and celery, and cook for 5 minutes.
In a large saucepan, melt 4 tablespoons butter on medium-low heat. Gradually add flour while whisking, and continue to whisk until the butter has absorbed all of the flour. Increase heat to medium and gradually whisk in milk and eggs. Continue cooking for 5 minutes, until sauce is smooth and slightly thickened. Season with salt, pepper, and garlic powder. Stir in tuna, water chestnuts, parsley, cooked onion mixture, and cooked noodles. Transfer to the prepared baking dish.
Melt remaining 2 tablespoons butter and mix with bread crumbs. Sprinkle cheese over casserole and top with bread crumbs. Bake for 45 minutes or until the casserole is bubbly around the edges.