Melt the butter in a large skillet over medium heat. Cook onion, bell pepper, celery, and garlic in butter until onions are tender. Stir in flour, and cook for 5 to 10 minutes, stirring frequently. Stir in crawfish. Cover, and simmer for 15 to 20 minutes, stirring often.
Stir in the processed cheese, half-and-half, Cajun seasonings, and cayenne pepper. Cover, and simmer for about 20 minutes, stirring occasionally.
Meanwhile, bring a large pot of lightly salted water to a boil. Cook pasta in boiling water for 8 to 10 minutes, or until al dente; drain.
Preheat oven to 350 degrees F (175 degrees C). Butter a 9x13 inch baking dish. Stir noodles into crawfish mixture; pour into prepared dish, and sprinkle with Parmesan cheese.
Bake in a preheated oven for 20 minutes, or until hot and bubbly.
