Adjust the oven rack to the middle position and preheat the oven to 400°F. While the oven is heating, bring a large pot of salted water to a boil and cook the egg noodles to al dente according to the package instructions. Drain the noodles well. Grease a 2-quart baking dish with a little melted butter to prevent sticking, then set it aside.

In a large mixing bowl, combine the cooked and drained egg noodles, condensed cream of mushroom soup, whole milk, drained peas, and drained tuna. Stir gently but thoroughly until everything is evenly mixed and coated. This will form the base of your casserole.

Transfer the noodle mixture from the mixing bowl to the greased 2-quart baking dish, spreading it out evenly. In a small bowl, stir together the plain dry breadcrumbs and melted butter until the crumbs are evenly coated. Set aside the breadcrumb mixture for topping later.

Place the assembled casserole (without the breadcrumb topping) into the oven and bake for 20 minutes. After 20 minutes, carefully remove the casserole from the oven and sprinkle the buttered breadcrumb mixture evenly over the top. Return to the oven and bake for another 5 minutes, or until the breadcrumb topping is golden brown and the casserole is hot and bubbling. When serving, season with kosher salt and freshly ground black pepper to taste. I like to let the casserole rest for a few minutes before serving to help it set and make it easier to scoop.