Step 1: Gather and Prep

• Gather all ingredients: 3 tablespoons unsalted butter, ½ cup finely diced yellow onion, 1 ½ teaspoons kosher salt, 3 tablespoons all-purpose flour, 4 cups cold milk, 1 cup shredded white Cheddar cheese, 12 ounces dry egg noodles, 2 (5.5 ounce) cans tuna packed in olive oil, ¾ cup frozen peas, 1 pinch cayenne pepper, ¼ teaspoon black pepper, ¼ teaspoon Worcestershire sauce, ½ cup plain bread crumbs, ½ cup grated Parmigiano-Reggiano cheese, and 2 tablespoons olive oil.
• Preheat the oven to 375°F (190°C). Lightly butter a 9×13-inch casserole dish.

Tip: Dice onions finely for even cooking and a smooth sauce.

Step 2: Make the Cheese Sauce

• Melt 3 tablespoons unsalted butter in a medium saucepan over medium heat.
• Add ½ cup finely diced yellow onion and ½ teaspoon kosher salt; sauté until soft and translucent, 3-4 minutes.
• Stir in 3 tablespoons all-purpose flour and cook, stirring, for 3 minutes, reducing heat if needed to avoid browning.
• Pour in 4 cups cold milk and whisk for 1 minute. Raise heat to medium-high and cook, stirring often, until the sauce thickens and simmers.
• Remove from heat and whisk in 1 cup shredded white Cheddar cheese until melted and smooth. Reserve the sauce.

Tip: Whisk constantly when adding milk to prevent lumps in the sauce.

Step 3: Cook the Noodles

• Bring a large pot of water with the remaining 1 teaspoon kosher salt to a rapid boil.
• Cook 12 ounces dry egg noodles for 5 minutes (1 minute less than package instructions for al dente).
• Drain well and transfer to a large mixing bowl.

Tip: Undercook noodles slightly to keep them firm after baking.

Step 4: Combine Ingredients

• Add the reserved cheese sauce to the noodles in the mixing bowl.
• Stir in 2 (5.5 ounce) cans drained and crumbled tuna, ¾ cup thawed and drained frozen peas, 1 pinch cayenne pepper, ¼ teaspoon black pepper, and ¼ teaspoon Worcestershire sauce.
• Mix with a spatula until evenly combined.

Tip: Mix gently to avoid breaking the noodles or tuna too much.

Step 5: Assemble and Top

• Pour the mixture into the prepared 9×13-inch casserole dish, spreading evenly.
• In a small bowl, mix ½ cup plain bread crumbs, ½ cup grated Parmigiano-Reggiano cheese, and 2 tablespoons olive oil until it resembles wet sand.
• Sprinkle the breadcrumb mixture evenly over the casserole.

Tip: Ensure the topping is evenly distributed for a consistent crunchy crust.

Step 6: Bake and Serve

• Bake in the center of the preheated oven for 30 minutes, until the top is browned and bubbly.
• Let the casserole rest for 10 minutes before cutting and serving.

Tip: Resting allows the casserole to set, making it easier to serve neat portions.