Melt butter in a skillet set over medium heat. Add onion, red pepper, banana or poblano pepper, and white onion parts and sauté until onion is translucent, 6 to 8 minutes. Add crawfish, Creole seasoning, and corn kernels and cover; cook for 5 minutes. Stir in cream (if the crawfish had a lot of fat, 1 cup should be sufficient; add more if it’s dry), bring to a bare simmer, and taste; add salt, pepper, and cayenne as desired; taste and add a splash of vinegar if it needs a little lift.

Stir in parsley and basil and serve at once.