I place the chicken breast in a pot of water and bring it to a gentle boil (not a raging boil — that keeps it tender). After about 15 minutes (when it’s fully cooked), I shred it with forks. Then I toss the shredded chicken with blue cheese (or ranch) dressing and set it aside to infuse flavor.
In the large skillet, I melt butter over medium heat, then sauté the onion and celery until softened (around 5 minutes). I add garlic for a minute more. Then I pour in the undrained diced tomatoes plus the chicken broth, bring that to a boil, and nestle the uncooked penne into it. I partially cover the pan and let it cook for 10–13 minutes (stir gently beneath the lid occasionally) until the pasta is al dente.
Once the pasta is cooked, I reduce heat to low and stir in buffalo sauce, softened cream cheese cubes, shredded cheddar, and mozzarella. Stir gently until it becomes creamy. Then I fold the shredded chicken into the sauce. If desired, I swirl in 2 Tbsp of cold butter at the end to get a silky finish (a chef’s trick called monter au beurre).