Preheat your oven to 190°C (375°F). Lightly grease a 2-quart (approximately 2-liter) baking dish with butter or cooking spray.

Cook the egg noodles according to package directions until al dente. Typically, this involves boiling them in generously salted water for 7-10 minutes. Drain the noodles thoroughly and set aside. Do not rinse them, as the starch helps the sauce adhere.

While the noodles are cooking, prepare the creamy sauce. In a large skillet or pot, melt the 50g (3.5 tbsp) of butter over medium heat. Once melted and shimmering, add the finely chopped yellow onion and finely chopped celery. Sauté for 5-7 minutes, stirring occasionally, until the vegetables are softened and the onion is translucent. Be careful not to brown the vegetables.

Sprinkle the 50g (0.4 cup) of all-purpose flour over the softened vegetables and butter. Whisk continuously for about 1-2 minutes to cook out the raw flour taste and form a roux. This will help thicken the sauce.

Gradually pour in the 500ml (2 cups) of milk, whisking constantly to prevent lumps. Continue to cook and stir the sauce over medium heat until it thickens to a smooth, creamy consistency, which should take about 5-8 minutes. The sauce should coat the back of a spoon.

Stir in the drained and flaked tuna, frozen peas, 5g (1 tsp) of salt, 2g (0.5 tsp) of freshly ground black pepper, and 15ml (1 tbsp) of Worcestershire sauce. Mix everything together until well combined and heated through, about 2-3 minutes. Taste and adjust seasoning if necessary.

Add the drained egg noodles to the skillet with the tuna mixture. Gently fold them in until evenly coated with the creamy sauce. Ensure all the noodles are incorporated.

Pour the entire mixture into the prepared baking dish, spreading it evenly. The dish should be filled to about 2.5cm (1 inch) from the rim.

Evenly sprinkle the 100g (3.5 oz) of crushed potato chips over the top of the casserole. Press them down slightly to ensure they adhere to the sauce and will create a crispy layer.

Bake in the preheated oven for 20-25 minutes, or until the casserole is bubbling around the edges and the potato chip topping is golden brown and crispy. Keep an eye on the chips to prevent burning.

Remove the casserole from the oven and let it rest for 5-10 minutes before serving. This allows the sauce to set slightly, making it easier to serve.