1 T. olive oil
1 T. butter
2 celery stalks, diced fine (about 2/3 c.)
1 bunch of scallions, white and light green parts only, thinly sliced
1 c. diced mushrooms
1 1/2 t. Old Bay seasoning
2 T. flour
1 3/4 c. milk
salt and pepper to taste
1/4 c. sour cream
1 T. Dijon mustard
6 oz. flat egg noodles
3/4 c. coarsely grated Parmesan
6 oz. chunk white tuna
1/4 c. Parmesan
1 T. minced fresh parsley
1 c. crumbled potato chips
Preheat oven to 350 F.
Butter an 8-inch square glass baking dish and bring a large pot of water to a boil.
Heat olive oil and butter in a medium-large skillet over medium heat.
When the oil is hot and the butter foams, add celery and cook, stirring occasionally, until softened but not browned.
Stir in scallions and mushrooms and cook about 5 minutes.
Add Old Bay seasoning and flour, stir until well mixed, and cook for 2 minutes.
Slowly add milk, stirring well to make sure no lumps form.
Bring mixture to a boil, reduce heat to medium-low, and simmer, stirring occasionally, until slightly thickened.
Remove from heat and adjust seasoning.
Stir in sour cream and mustard.
When water comes to a boil, add noodles and cook until slightly tender but still white in the middle. Drain.
Stir cheese and noodles into the mixture.
Flake tuna into mixture and stir gently.
Pour everything into prepared baking dish.
Combine the topping ingredients and sprinkle over casserole.
Cook until topping is golden brown, about 30-40 minutes.