– 1 16-oz pack fettuccine – 1/2 cup unsalted butter – 1/2 red bell pepper, chopped – 1 celery, chopped – 1 onion, chopped – 6 garlic cloves, minced – 1 lb frozen crawfish, thawed – 2 tsp Cajun seasoning – 1/2 tsp ground black pepper – 3 tbsp all-purpose flour – 3/4 cup half and half – 1/2 cup sour cream – 4 oz Velveeta cheese, cubed – 2/3 cup parmesan cheese, freshly grated – 2 green onions, sliced – 2 tbsp freshly chopped parsley