In a large pot, fill the pan with water and cook the rotini pasta according to the package directions until al dente, drain well, reserving one cup of the pasta water in case you need to thin the sauce. Reserve the pasta in the stock pot for later. (Keep it covered with a lid to maintain warmth.
In a large saute pan or large skillet, heat the 3 tablespoons of butter and a drizzle of olive oil, over medium heat. Add the small diced shallots and toss in the butter. Cook for 2-3 minutes until translucent and soft. Add in the garlic. Stir the garlic until fragrant.
Add in the brandy or wine (if you are using it, if not move on to the next step) to deglaze the pan and stir and simmer until the pan is nearly dry and all of the liquid from the alcohol is nearly evaporated. You can turn the pan up to medium-high heat to move this along if you wish.
Pour in the 2 cups of heavy cream and 1 lb crawfish tails and increase the heat to high. Whisk in the parmesan cheese, cajun seasoning, and black pepper, then season with salt if needed, and stir in the fresh lemon juice. Add red pepper flakes if you like spicier pasta sauce.
Reduce the heat and simmer this mixture for 5-10 minutes to allow the flavors to develop. Taste for seasoning and make any adjustments. Pour the completed sauce over the reserved cooked pasta, and toss well.
At New Orleans Jazz Fest the garnishes of green onion and parsley are folded into the pasta at this point, but you can serve them on top if you like, or leave them out for guests who don’t like them (aka kids).
If you need to thin the sauce you have the reserved pasta water. Add it in 2 tablespoons at a time until you have achieved the right consistency and re-test for seasoning before serving.
Serve hot from the pan with garlic bread, a green salad, and your favorite Mardi Gras drinks!