Heat olive oil in a large pot over medium heat. Sauté onion, celery, and carrot until softened, about 5 minutes. Add garlic and cook for an additional minute.
Stir in tomato paste, paprika, cayenne (if using), and season with salt and pepper. Cook for 2 minutes, stirring constantly.
Sprinkle flour over the mixture, stirring until well combined. Cook for another minute.
Gradually add broth, stirring continuously to prevent lumps. Simmer on low heat for 10 minutes, stirring occasionally.
Puree the soup until smooth using an immersion blender, or transfer to a standard blender in batches.
Mix in the heavy cream and simmer for 10 more minutes, until slightly thickened.
Add crab meat, shrimp, and sherry (if using). Simmer for 5 minutes or until seafood is heated through, keeping the heat low to avoid curdling the cream.
