Preheat oven to 350F.Cook noodles in salted water for one minute less than package directions. Drain, add one tablespoon of butter, mix, and set aside.
Grate cheese, dice green onions, cut cream cheese into cubes, and set aside. Begin to melt 4 tbsp (1/4 cup) of butter in a saucepan on medium heat.
When the butter is melted, add the diced green onion, garlic powder, onion powder, and salt. Cook on medium-high until onions are fragrant and soft, about 2-3 minutes. Stir regularly.
Next, whisk the flour into the melted butter mixture. Once the butter and flour are mixed and begin to form a paste, SLOWLY add the milk and cream. Stir constantly, and let the sauce thicken for at least five minutes. Don't skip this step!
Once the roux is gently bubbling and has thickened up a little bit, add the cubed cream cheese and cook on low heat for a few minutes until melted. Once the cream cheese has melted, turn off the heat. Now, add shredded cheese and stir gently, allowing the remaining heat in the roux to melt the cheese - this stops it from getting stringy. Once the cheese has all melted, add the sour cream and stir to incorporate.
In a bowl, mix 1 cup of crushed sour cream and onion chips with 1 tbsp. of melted butter. Use more chips if you want a denser topping.
When the roux and macaroni are done, combine in a greased baking dish. Top with chip mixture, COVER, and bake at 350F for about 15 minutes.
You can add more green onions for garnish if you'd like. Then, serve, enjoy, and prepare to amaze your dinner guests!