Heat the butter in a large pot over medium-high heat. Add the scallion whites, celery and bell pepper and cook, stirring occasionally, until the vegetables are crisp-tender, about 4 minutes. Add the flour and Old Bay Seasoning and cook, stirring, until the flour is lightly toasted, about 1 minute. Add the milk, 6 cups water and the rice. Bring to a rapid simmer, then reduce the heat to medium and cook until the rice is tender, about 15 minutes. Add the corn to the pot and cook 3 minutes. Stir in the shrimp and cook until they curl and turn opaque, about 3 more minutes. Season the chowder with salt and pepper and stir in the sherry. Ladle into bowls and top with the scallion greens.
Photograph by Antonis Achilleos
Courtesy of Food Network Magazine