Preheat oven to 375 degrees F and grease casserole or cast iron skillet with butter. Set aside.
Bring a large pot of water to a boil. Once the water is boiling, add dried pasta and cook for 7 minutes. Pasta should be al dente so that it's not completely cooked.
Drain water and add macaroni in a large bowl.
Grate both sharp and mild cheeses.
In a large saucepan, melt butter and add flour to make a roux.
Once the roux is smooth whisk in the milk and heat on high until the milk begins to boil.
Turn off the heat and add 2 cups of sharp cheddar cheese and 1 cup of mild cheddar cheese to the milk and stir until smooth.
Add salt, black pepper and cajun seasonings to the cheese mixture. Before proceeding to next steps, taste the cheese sauce for extra seasoning.
In the large bowl, pour the cheese over the macaroni and mix well.
Begin to add sour cream to macaroni and mix well.
In a small bowl, whisk one large egg and add to the mac and cheese mixture.
Next, pour the macaroni mixture into the baking dish.
Sprinkle the remaining mild cheddar on top of pasta.
Optional, sprinkle paprika seasoning on top of pasta.
Bake macaroni for 40 minutes or until cheese is bubbly or golden brown.