Cook the egg noodles according to the package directions, stopping 3 minutes early so they stay firm. Drain, rinse with cold water, and set aside.
12 ounces egg noodles
In a large pot, melt butter over medium heat. Add the onions and celery, cooking until softened, about 5 minutes. Stir in the flour and cook for 3 minutes on low heat, stirring often to avoid sticking or burning.
¼ cup unsalted butter, 2 cups onions, 1 cup celery, ¼ cup all-purpose flour
Slowly whisk in the milk, cream, and chicken stock, ensuring the mixture stays smooth. Stir in the oregano and mustard, then bring the sauce to a gentle simmer. Cook for 5-8 minutes, stirring occasionally, until thickened.
1 ½ cups milk, ¼ cup heavy cream, 2 cups chicken stock, 2 teaspoons dry oregano, 2 tablespoons whole-grain mustard
Add the grated Gruyere cheese, stirring until melted, then mix in the shredded chicken. Season with salt and pepper to taste. Combine the noodles with the chicken sauce, stirring until fully coated. Transfer the mixture to a casserole dish that fits in your air fryer.
6 ounces Gruyere cheese, 3 cups cooked chicken, Salt and pepper
In a small bowl, mix the panko breadcrumbs with the melted butter. Spread the breadcrumbs evenly over the casserole.
½ cup panko breadcrumbs, 1 tablespoon butter
Air fry at 325°F (160°C) for 6 minutes or until the topping is golden brown and crispy. Garnish with chopped parsley and serve immediately.