Step 1

In a large soup pot, melt the butter. Add the onion, celery, scallions and bay leaves and cook over moderate heat until softened, 5 minutes. Stir in the flour and cook, stirring, for 2 minutes. Gradually whisk in the chicken broth and bring to a boil. Simmer, stirring occasionally, until the broth is thickened and the vegetables are very tender, 15 minutes.

Step 2

Add the roasted garlic and milk; bring to a simmer. Stir in the sherry, ketchup, tomato paste, paprika, cayenne, cloves, mace, nutmeg, cream and Tabasco and bring to a simmer. Season with salt and pepper, then add the crab; simmer until hot. Discard the bay leaves. Serve the bisque with oyster crackers.