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 Essence, and cook, stirring, for 1 minute. Add the corn and cook, stirring, until fragrant and just golden, about 5 minutes. Add 1/4 cup of the chicken stock and cook until almost all evaporated, about 2 minutes. Add the remaining 1/4 cup of stock and cook until almost all evaporated, about 2 minutes. Add the crawfish, remaining 2 teaspoons of Essence, 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 and serve with rice, garnished with the green onions and tomato concasse.