Cook the pasta to al dente according to the package directions and set aside.
Sprinkle the crawfish tails with Creole seasoning and set them aside.
Prepare the jalapeno pepper by slicing in half lengthwise and removing the seeds and membrane. Finely chop.
Grate the cheeses, measure the other ingredients and set them aside. Prepare a casserole dish by spreading softened butter on the inside.
Preheat the oven to 350 degrees Fahrenheit.
Start with a cold Dutch oven. Add the heavy cream, melted butter and eggs to the Dutch oven off the heat. Whisk together until all are combined thoroughly.
When the cream, eggs and butter are completely combined, move the Dutch oven over medium heat and slowly warm the cream mixture, stirring or whisking constantly until a slight simmer develops.
Add the Pepper Jack Cheese and 2 cups of the Cheddar Cheese (reserve the remaining cheese for the top) and stir to combine the cheese into the cream sauce.
Continue to stir as the cheese melts.
Add the Creole seasoning, kosher salt, white peppers, dry mustard, chopped pimentos and chopped jalapenos (if using). Mix together thoroughly.
Add the crawfish tails and stir until evenly distributed throughout the cheese sauce.
Simmer the cheese sauce on low heat for a minute or two.
Add about half the pasta and stir until coated in the cheese sauce. Continue adding pasta a little at a time, stopping when the macaroni is creamy and heavily coated. You may not need all the pasta.
Turn the macaroni and cheese mixture into a baking casserole dish that has been prepared by coating the insides with softened butter.
Spread the remaining Cheddar Cheese evenly on top and sprinkle about 2 tablespoons of breadcrumbs (if using) evenly on top, then place small pats of butter on top of that.
Bake uncovered for about 20 minutes, or until the cheese topping is melted and lightly browned. Let rest for 5 minutes before serving.
Remove the casserole from the oven and let it sit for about 5 minutes, then serve.
Notes
Read my article Crawfish Mac and Cheese, for step-by-step photos, tips, and FAQs.Use Louisiana crawfish tails whenever possible. Leftover crawfish boil tails add extra Cajun flavor.For less heat, leave out the jalapenos and substitute Monterey Jack for the Pepper Jack cheese.Sharp Cheddar and Pepper Jack make a rich, creamy cheese sauce, but other melty cheeses like Gouda, Gruyere, Fontina, or Monterey Jack also work well.Add the pasta a little at a time and stop when the macaroni is creamy and well-coated. You may not need all the pasta.If substituting pasta, use a sturdy shape like rotini, bowtie, long macaroni, or fettuccini so the sauce has plenty of surface to cling to.Store leftovers in an airtight container in the refrigerator for 3 to 5 days or freeze for up to 3 months. Defrost overnight in the refrigerator before reheating.Reheat covered in a 350-degree oven until heated through to 165 degrees internally, or reheat individual portions in the microwave.