Pre-heat your oven to 350°F.
Cook the pasta according to the package directions, minus one minute from al dente. Drain the pasta in a colander, then set it aside until ready to use.
Cut the chicken into small one-inch pieces. Then, add two tablespoons of unsalted butter to a large oven-proof skillet* set over medium heat. Once the butter has melted, add the cut chicken pieces. Cook for five to six minutes, stirring occasionally, until the chicken pieces have turned from pink to white. Then, using a slotted spoon, remove the cooked chicken from the pan and transfer it to a paper towel-covered plate. Set aside until ready to use.
Add the rest of the butter to the hot pan. Once the butter has melted, reduce the heat to medium-low and add the all-purpose flour, salt, pepper, and ground mustard. Then, quickly stir it all to form a light roux.
After the roux has been formed, add the whole milk and whisk until thick and bubbly.
Then, add six ounces of freshly shredded extra sharp cheddar cheese and whisk until all the cheese has fully melted and has started to turn gooey.
Next, add four ounces of freshly shredded Swiss cheese and whisk until the cheese has fully melted and the sauce has thickened.
Then, add the freshly shredded Parmesan cheese and whisk until the cheese has fully melted and the sauce is thick and gooey.
Next, add the Homemade Buttermilk Ranch Dressing** and whisk until the dressing is fully incorporated and the sauce is thick and creamy. Then, add the cooked and drained pasta, the cooked chicken and half of the crumbled bacon to the finished sauce. Using a rubber spatula, stir everything together until it's well combined and the pasta is fully coated in the sauce.
Once everything is well combined, top with a sprinkling of the remaining two ounces of Swiss cheese, two ounces of extra sharp cheddar cheese, and the other half of the crumbled bacon.
Bake in a 350°F oven for 30 minutes until the cheese has melted and it is hot and bubbly. Let stand for 5-10 minutes before serving.
Yield 6 servings.