Step 1

Add 8 cups water to large pot and place pot on stovetop over medium-high heat. Bring water to boil, then add ½-1 tablespoon salt. Stir to incorporate.

Step 2

When salted water begins to boil, add 8 ounces uncooked egg noodles and stir to incorporate. Boil noodles for shortest amount of time indicated on noodle packaging.

Step 3

Once noodles have boiled for desired length of time, immediately pour noodles and water into colander. Drain noodles very well, then transfer noodles to casserole dish. Set dish aside.

Step 4

Preheat oven to 350° Fahrenheit while preparing cream sauce.

Step 5

Add 5 tablespoons unsalted butter to medium saucepan and place pan on stovetop over low heat. Heat saucepan until butter is almost completely melted, stirring butter occasionally.

Step 6

Once butter is just melted, add 5 tablespoons all-purpose flour to saucepan. Vigorously whisk butter and flour together until fully incorporated into smooth mixture.

Step 7

Cook flour mixture over low heat approximately 1 minute, stirring constantly, until mixture turns golden and begins to bubble.

Step 8

Remove saucepan from heat. Slowly add 2 ½ cups whole milk in small increments, whisking constantly to incorporate each addition.

Step 9

When all milk has been added, return saucepan to heat and increase heat to medium. Simmer mixture over medium heat, whisking constantly, until mixture has thickened and begins to bubble.

Step 10

Add ½ teaspoon salt, ¼ teaspoon freshly ground black pepper, ½ teaspoon garlic powder, and 1 teaspoon dried parsley (optional) to thickened sauce mixture, whisking gently to incorporate spices.

Step 11

Remove saucepan from heat. Add 1 cup shredded fresh cheddar cheese in small increments, whisking constantly, until all cheese has been incorporated and melted.

Step 12

Immediately pour prepared cheese sauce over egg noodles in baking dish, then add 1 5-ounce can chunk light tuna in water (drained) and ¾ cup frozen green peas.

Step 13

Gently stir ingredients together until well blended and fully covered in cheese sauce. Once incorporated, spread mixture out evenly to cover entire bottom of casserole dish, making sure to reach all sides of dish.

Step 14

Place casserole dish in preheated oven. Bake casserole 15 minutes while preparing breadcrumb topping.

Step 15

Place 1 tablespoon unsalted butter in small, microwave-safe bowl. Microwave butter in 15-second increments, stirring well between each burst, until butter is melted but not bubbling or boiling. Carefully remove bowl from microwave.

Step 16

Add 2 tablespoons breadcrumbs and 1 large pinch salt to bowl with melted butter. Stir ingredients together until well blended, with all breadcrumbs completely buttered.

Step 17

After casserole has baked 15 minutes, remove casserole dish from oven. Sprinkle ½ cup shredded fresh cheddar cheese across top of dish, covering entire casserole evenly, then sprinkle prepared breadcrumbs evenly over layer of shredded cheese.

Step 18

Return baking dish to oven. Bake casserole 5 minutes more or until cheese layer is melted and bubbly, then carefully remove dish from oven and set aside. Let casserole rest 3 to 5 minutes.

Step 19

Garnish casserole with chopped fresh parsley if desired and serve warm with preferred sides.