Buffalo Chicken Pasta loaded with creamy sauce and tender chicken

Ingredients

• 1/2 cup ranch dressing
• 1 cup mozzarella, shredded
• 225g cream cheese, soft and cubed
• 1/2 cup buffalo sauce (like Frank's Red Hot)
• 1 cup cheddar, shredded
• 3 cups cooked chicken breast, diced
• 3 1/2 cups uncooked rotini
• 1 can diced tomatoes (about 410g), undrained
• 3 cups chicken broth
• Pinch of chili flakes (optional)
• 1/4 teaspoon black pepper
• 1/2 teaspoon salt
• 3 cloves garlic, minced
• 1/2 cup celery, diced
• 1 cup onion, chopped
• 2 tablespoons butter