Step 1

In a large pot, melt the butter over medium heat. Add the onion, celery, and scallions and cook until soft, about 5 minutes. Stir in the flour and cook, stirring constantly, for about 2 minutes. Gradually whisk in the broth and bring to a boil. Reduce the heat to medium-high and simmer, stirring occasionally, until the broth thickens and the vegetables are tender, about 5 to 7 minutes. Reduce the heat to low and whisk in the sherry, ketchup, tomato paste, seafood seasoning, and cream.

Step 2

Bring to a simmer, but do not let it boil. Season with salt and pepper to taste, then add the crab and shrimp. Cook just until the crab and shrimp are warmed through, about 5 more minutes.

Step 3

Ladle into individual bowls and garnish with additional sliced scallions or fresh herbs, if desired.