In a large pot over medium-high heat, melt butter. Once hot, add onion, cajun seasoning, and garlic; cook until tender.
Add sausage and cook for 3-5 minutes, until browned.
Add half and half, chicken broth, and pasta. Bring to a boil, then reduce heat to medium-low and cook for about 6-8 minutes, until pasta is al dente.
Stir in crawfish tails, lemon juice, half of the parsley, half of the green onions, and half a cup of shredded parmesan cheese until blended and melted. Cover the dish with the rest of the cheese and put it under a broiler for 4-6 minutes, until the cheese on top is melted, browning, and bubbly.
Garnish with remaining green onions and parsley.
Notes
Make sure your cooking dish is oven-safe - this will take you from stove to oven without having to use another dish!
If you finish cooking and find that the sauce is too thick, add another ½ cup of half and half. Alternatively, if it's too soupy, cook the pasta/sauce combo for another minute or two. (It might be a little soupier than preferred when it goes into the oven - that's ok! It will thicken some more.)
This one definitely needs to be stored in the refrigerator. Make sure it's in an airtight container - those flavors are strong and will seep into other foods! Enjoy this one within 2-3 days of cooking it.
This dish makes a ton of food - feel free to halve the recipe if needed! The ingredient portions just work out better with a full recipe.