Roast the corn in a 350 degree oven in the husk for 45 minutes.  Once cooked remove from the oven and let cool.  Once cool remove the husk and then cut the corn from the cob. 

In a large saucepan or skillet, melt the butter over medium-high heat. Add the onions, celery, and bell peppers, and cook, stirring, until soft, about 3 minutes. Add the garlic and 1 teaspoon of the Cajun seasoning, and cook, stirring, for 1 minute. 

Add the corn and cook, stirring, until fragrant and just golden, about 5 minutes. Add the crawfish, remaining 2 teaspoons of Cajun seasoning, and salt, and cook, stirring, for 1 minute. Add the cream, bring to a boil, and cook until the crawfish are warmed through and the sauce is thickened, 3 to 4 minutes.

Remove from the heat, garnished with the green onions and serve.