Bring enough salted water to a boil in a large saucepan to cover your pasta and cook as directed on the package minus 2-3 minutes short of al dente.
Drain the pasta and place back in the saucepan. Toss the cooked pasta with 1 tbsp of butter to coat it. Tossing the butter into the pasta prevents it from absorbing liquid while baking and keeps it from getting soggy.
Heat oven to 350 degrees.
In a large oven proof skillet (I use a Lodge 12" cast iron skillet), melt 4 tbsp of butter over medium high heat.
Add the flour and stir into the butter. Saute the mixture for 2-3 minutes, stirring frequently. It will be a thick pasty consistency and become slightly browned and nutty smelling. Watch it closely and reduce heat if needed.
Add the milk slowly a little at a time and stir each addition of milk into the flour mixture. Whisk the sauce and cook over medium heat until thick and smooth. Do not boil.
Add salt, pepper, mustard powder and cayenne pepper (optional) and stir in to the sauce until combined.
Whisk the green chiles and 2 tbsp salsa verde into the sauce.
Start adding the cheese, including 1 cup of mozarella cheese a handful at a time and whisk into the sauce until smooth and melted. (Reserve 1/2 cup of colby for the top.)
Taste and add additional salt and pepper to taste if needed.
Stir the macaroni or pasta into the cheese sauce.
Cover the top of the macaroni with grated parmesan cheese and the reserved 1/2 cup of your grated cheese.
Sprinkle the top with dried parsley.
Bake for about 30 minutes until bubbly and cheese topping is golden brown. You may place it under the broiler for 2-3 minutes if desired for an extra crispy golden crust topping if desired. Watch closely.
Store in covered container in refrigerator for 3-5 days.