Step 1: Cook the Noodles
Bring a large pot of salted water to a boil. Cook the egg noodles according to the package instructions until al dente. Drain and set aside.

Step 2: Sauté the Vegetables
In a large skillet, melt the butter over medium heat. Add the diced onion and celery, sautéing for 4-5 minutes until softened. Add the garlic and cook for an additional 1 minute, stirring constantly to avoid burning.

Step 3: Make the Sauce
Sprinkle the flour over the vegetables and stir to coat evenly. Cook for 1-2 minutes to eliminate the raw flour taste. Gradually whisk in the milk and broth, ensuring no lumps form. Add the salt, black pepper, and dried thyme. Cook for 5-7 minutes, stirring frequently, until the sauce thickens.

Step 4: Add Cheese and Tuna
Remove the skillet from the heat and stir in the shredded cheddar cheese until melted and smooth. Add the frozen peas and flaked tuna, mixing gently to combine.

Step 5: Combine with Noodles
In a large mixing bowl, combine the cooked noodles with the sauce mixture, tossing to coat evenly. Transfer the mixture to a greased 9×13-inch baking dish.

Step 6: Prepare the Topping
In a small bowl, mix the panko breadcrumbs with the melted butter, grated Parmesan cheese, and dried parsley. Sprinkle the breadcrumb mixture evenly over the casserole.

Step 7: Bake
Preheat your oven to 375°F (190°C). Bake the casserole, uncovered, for 20-25 minutes, or until the topping is golden brown and the casserole is bubbly.

Step 8: Serve
Let the casserole rest for 5 minutes before serving. Enjoy your Tuna Noodle Casserole warm and creamy, with a satisfying crunch from the topping.