Step 1: Cook the pasta. Bring a large pot of salted water to a rolling boil. Add 1 pound of elbow macaroni or your preferred pasta and cook according to package directions until al dente. Drain well and set aside. Do not rinse the pasta; the starches help the sauce adhere.
Step 2: Shred the cooked chicken. If you're using pre-cooked chicken, shred it into bite-sized pieces. If cooking fresh chicken, season and bake or boil chicken breasts until cooked through, then shred.
Step 3: Combine chicken and BBQ sauce. In a medium bowl, toss the shredded chicken with 1 cup of your favorite BBQ sauce until well coated. Set aside.
Step 4: Prepare the roux. In a large, deep pot or Dutch oven, melt 1/2 cup (1 stick) of unsalted butter over medium heat. Once melted, gradually whisk in 1/2 cup of all-purpose flour. Cook, stirring constantly, for 1-2 minutes until a thick paste forms and the raw flour smell is gone. This is your roux, the base of a creamy sauce.
Step 5: Add milk. Slowly whisk in 4 cups of whole milk, a little at a time, ensuring no lumps form. Continue whisking until the sauce is smooth and begins to thicken, about 5-7 minutes. Bring it to a gentle simmer, but do not boil.
Step 6: Introduce the cheese. Reduce the heat to low. Add 4 cups of grated cheese (sharp cheddar, smoked Gouda, Monterey Jack blend) to the sauce, a handful at a time, whisking until each addition is fully melted and incorporated before adding more. This gradual melting ensures a super smooth sauce for your BBQ Chicken Mac and Cheese. Season with 1 teaspoon of salt, 1/2 teaspoon of black pepper, 1/4 teaspoon of garlic powder, and a pinch of cayenne pepper (optional, for a little kick). Taste and adjust seasonings as needed.
Step 7: Combine pasta and sauce. Add the drained cooked pasta to the cheese sauce and stir gently until every noodle is thoroughly coated.
Step 8: Layer for baking. Pour half of the mac and cheese mixture into a greased 9x13 inch baking dish. Evenly spread the BBQ chicken mixture over the mac and cheese layer. Top with the remaining mac and cheese.
Step 9: Add a crunchy topping (optional). For an extra layer of flavor and texture, sprinkle an additional 1 cup of grated cheese over the top, along with 1/2 cup of panko breadcrumbs mixed with a tablespoon of melted butter.
Step 10: Bake. Preheat your oven to 375°F (190°C). Bake the BBQ Chicken Mac and Cheese for 25-30 minutes, or until the top is golden brown and bubbly. If the topping browns too quickly, you can loosely tent it with foil.
Step 11: Rest and serve. Remove from the oven and let it rest for 5-10 minutes before serving. This allows the sauce to set slightly, preventing it from being too runny. Garnish with fresh chopped chives or parsley, if desired.