Start by cooking the pasta. Bring a large pot of salted water to a boil and add the shell pasta. Cook just until al dente, according to package instructions. You want it slightly firm, as it will continue cooking in the oven. Drain and set aside.
Next, let’s sauté the veggies. In a large skillet, melt 1 tablespoon of butter over medium heat. Add the celery, onion, peas, and garlic. Sauté for about 5 minutes, until the vegetables are tender and fragrant. Remove from heat and set aside.
Now it’s time to make the sauce. In the same skillet, add the remaining 3 tablespoons of butter. Once it’s melted, sprinkle in the flour and cook, stirring continuously for about 1 minute to create a roux. It should smell nutty, but be careful not to let it brown.
Slowly whisk in the chicken broth and milk. Continue stirring until the mixture is smooth and free of lumps. Bring it to a simmer and keep stirring until it thickens slightly. This should take about 3 to 5 minutes.
Reduce the heat to low, and add the kosher salt, black pepper, dill weed, lemon juice, parsley, and 1/2 cup of the parmesan cheese. Stir well, and taste to adjust the seasoning if necessary. This is your creamy sauce that will bring everything together!
Now, it’s time to combine. Remove the sauce from the heat and stir in the cooked pasta, sautéed vegetables, and tuna. Mix everything gently until well combined. You should see that luxurious sauce coating each piece of pasta.
Transfer the mixture to a greased 9×13 inch baking dish, spreading it evenly. Sprinkle the top with the remaining parmesan cheese for that cheesy crust.
For the topping, crush the Ritz crackers and mix them with the melted butter. Sprinkle this mixture evenly over the casserole. This will create a deliciously crunchy texture on top.
Finally, bake in a preheated oven at 350°F (175°C) for 25 to 30 minutes. You want the top to be golden brown and the casserole bubbly. Keep an eye on it to avoid over-browning.
Once baked, remove it from the oven and let it sit for a few minutes before serving. This will help the casserole set slightly, making it easier to scoop. Enjoy your Tuna Noodle Casserole warm!