Preheat oven to 350°F (175°C).

Cook pasta until al dente, drain well, and place in a large mixing bowl.

Season shrimp and crawfish lightly with Cajun seasoning if using.

In a large skillet, melt 2 tbsp of butter over medium-high heat. Add shrimp and sauté for 2–3 minutes per side until just cooked through. Set aside.

In the same pan, add 1 tbsp butter and lightly warm the crawfish for 1–2 minutes. Set aside.

In a large saucepan, melt the remaining 3 tbsp butter over medium heat. Whisk in the flour and cook for 1 minute to form a roux.

Slowly pour in evaporated milk and whole milk, whisking constantly until thickened (about 4–5 minutes).

Stir in garlic powder, onion powder, paprika, salt, and black pepper.

If using cheeses, add white cheddar, mild cheddar, and half of the mozzarella, stirring until melted and smooth. For a non-dairy or lighter version, skip the cheeses and proceed to the next step; the sauce will be thinner but still creamy from the sour cream.

Add sour cream to the sauce and stir to combine.

Pour the sauce over the cooked pasta and stir until fully coated.

Gently fold in shrimp and crawfish tails.

Pour the entire mixture into a buttered deep 9×13 or large aluminum baking pan.

If using cheese, top evenly with the remaining mozzarella cheese and a light sprinkle of paprika. If not using cheese, simply sprinkle with paprika.

Bake uncovered at 350°F for 25–30 minutes or until hot, bubbly, and golden on top.

Garnish with chopped parsley before serving.