Make the corn wafers:
In a bowl with an electric mixer cream the butter, add sugar, and beat the mixture until it is light and fluffy. Add the egg white and salt and beat the mixture at low speed for 5 seconds, or until it is just combined. The mixture will be lumpy. Add the cornmeal, flour and Parmesan and stir the mixture until it is just combined. Transfer the mixture to a small bowl and chill it, covered, for at least 4 hours or overnight. Arrange rounded teaspoons of the mixture 3 inches apart on buttered baking sheets and with a fork dipped in cold water flatten them carefully to form 2-inch rounds. Bake the wafers in batches in the middle of a preheated 425 degree oven for 5 to 6 minutes, or until the edges are golden brown, with a spatula transfer the wafers immediately to racks, and let them cool.
In a 9-inch cast iron skillet heat the oil over moderately high heat until it is hot but not smoking and in it brown the chicken, patted dry and seasoned with salt and pepper, in batches, transferring it as it is browned to a bowl. To the fat remaining in the skillet add the butter and flour and cook the roux over moderately low heat, stirring constantly, until it is the color of peanut butter. Stir in the onion, bell pepper, and celery and cook the mixture, stirring occasionally, until the vegetables are softened. Add the broth, tomatoes, chili powder, and chicken with any juices that have accumulated in the bowl, simmer the stew, covered, for 6 to 8 minutes, or until the chicken is cooked through, and stir in the corn. The stew may be prepared up to this point 1 day in advance and kept covered and chilled. Before serving, stir in the scallion greens and basil, season with salt and pepper, and serve it in bowls topped with the corn wafers.