Sprinkle in the 2 oz flour and cook for about 2 minutes, stirring constantly, letting it coat the vegetables. Pour in the 2 cups fish stock and 4 cups half-and-half, mixing well to avoid lumps.
Bring the soup to a gentle simmer and continue to cook for about 20 minutes, or until the potatoes are soft when pierced with a fork. Keep an eye on it to ensure it doesn't boil too vigorously.
Finally, stir in the 4 cups corn kernels, 1 pound lump crab meat, and 1/4 cup sherry. Let it simmer for another 5 minutes, just until everything is heated through. Taste and adjust the seasonings as needed, then remove the bay leaves before serving. Ladle the hot chowder into bowls; a few dashes of hot sauce on top are a nice touch if you like a little heat.