Preheat oven to 350°F (175°C). Grease an 8x8 inch baking dish.

Bring a large pot of salted water to a boil.

Heat olive oil and 1 tbsp butter in a medium saucepan over medium heat.

Add diced celery and cook until softened, about 5 minutes.

Stir in sliced scallions and minced jalapeno; cook for 3 minutes.

Mix in Old Bay Seasoning and flour until incorporated.

Cook for 1 minute, then slowly whisk in milk until smooth.

Bring to a boil, reduce heat, and simmer until thickened, about 5 minutes.

Season with salt and pepper.

Stir in sour cream and Dijon mustard.

Cook egg noodles in boiling water until al dente, about 3 minutes.

Drain the noodles.

Combine cooked noodles and 3/4 cup cheddar cheese into the vegetable-and-milk mixture.

Gently fold in the drained tuna.

Pour mixture into the prepared baking dish.

In a separate bowl, combine parsley, 2 tbsp butter, 1/4 cup cheddar, and crushed saltines.

Sprinkle the crumb mixture evenly over the casserole.

Bake for 20-25 minutes, or until golden brown and bubbling.