Preheat oven to 350.
Bring a large pot of water to a boil.
Cook noodles for 8 minutes. Drain and set aside.
Meanwhile, in a medium saucepan over medium heat, whisk together milk, sour cream, cream cheese, vanilla, 1/4 cup brown sugar, 1 teaspoon salt and 1 cup marshmallows. Cook until smooth. Remove from heat.
Add noodles, remaining marshmallows and chocolate chips. Fold gently to incorporate. Transfer to a greased 13x9-inch baking dish.
Combine butter and graham crackers in a medium bowl with remaining brown sugar and remaining salt. Crush to desired consistency.
Spread topping over noodles. Bake for 15 minutes, or until casserole is bubbling and topping is crisp.
