Begin the southern style mac by cooking the macaroni noodles. Grab a large stockpot or Dutch oven, fill it with water, and add lots of salt because it will help season the pasta. Allow the water to come to a boil before adding the 3 cups uncooked pasta.
Cook the pasta until it is just under al dente, it will fully cook once in the oven. It should still have a stiff bite to it. Carefully remove the pasta from the stovetop and drain off all of the water. Add it to a separate large mixing bowl while you continue with the rest of the recipe.
Preheat the oven to 375 degrees F. and butter the bottom and sides of a 9x13-inch baking/casserole dish. Set it aside.
Using the large stock pot over medium-high heat, add the 8 tablespoons butter and allow it to melt and become foamy. Add the 4 tablespoons all-purpose flour and stir or whisk continuously until it dissolves and thickens.
Slowly add the 2 cups half and half and 1 cup heavy cream, stirring the mixture continuously. Allow the mixture to cook for about 2 to 3 minutes.
Add in the ½ teaspoon dry mustard powder, ½ teaspoon garlic powder, 1 teaspoon salt, and 1 teaspoon ground black pepper and stir to combine.
Add the 4 cups shredded cheese and stir continuously to allow the cheese to completely melt to form the cheese sauce, this may take about 2 to 3 minutes.
Grab the cooked macaroni pasta that you set aside and add it to the cheese sauce. Stir until evenly distributed and the pasta is covered in the sauce. Pour the pasta into the prepared buttered baking dish.
Spread the pasta evenly into the bottom of the baking dish. Top with an even layer of 1 ½ cups shredded cheese. Place the macaroni into the oven to bake for about 15 to 20 minutes until golden brown and bubbly.
If you would like to brown the top of the mac and cheese, place it under the broiler on high for 2 to 3 minutes. Carefully remove it from the oven and allow it to cool for about 5 to 10 minutes before serving. Serve warm as a main dish or with your holiday meal or Sunday dinner and enjoy!