Preheat oven to 350°F. Brush a 12 inch cast iron skillet with 1/2 Tbsp softened butter, reserving remaining 1 1/2 Tbsp for top. Set aside. (Alternately, bake in any similar size oven safe skillet or 13 x 9 inch baking dish)
Cook macaroni in salted water per the package instructions until al dente. Drain well, then add to a large mixing bowl.
Meanwhile, in a 4 quart heavy bottomed saucepan, melt 1/2 cup butter over medium heat. Add flour, mixing until flour is absorbed. Cook for 1 minute, while stirring.
To the saucepan add, Dijon, salt, pepper, paprika, nutmeg and a dash or two, of hot sauce. Mix well. Gradually whisk in milk.
Increase heat to medium-high and bring to a boil, stirring constantly. Immediately turn the heat to low. Simmer gently bubbling for 5 minutes. Stir periodically to prevent sticking.
Toss together all three varieties of shredded cheese. Add 4 cups to sauce. Mix until completely melted, remove from heat.
Pour cheese sauce over cooked pasta in mixing bowl, mix until evenly coated.
Pour half macaroni into buttered cast iron skillet. Sprinkle with 1 cup shredded cheese blend. Pour remaining macaroni evenly on top.
Sprinkle macaroni with remaining 1 cup shredded cheese. Dot the top with reserved 1 1/2 Tbsp butter.
Bake for 35-40 minutes until bubbly and golden.
Let stand on counter for 10 minutes, then serve.