In a medium pot, melt 4 tbsp butter over medium heat. Add onions, celery and carrots. Sauté 5 - 6 minutes, until onions just begin to soften.
Add garlic, tomato paste, thyme, salt and pepper to the pot. Sauté for another 5 minutes, stirring frequently.
Sprinkle 4 tbsp flour into pot and stir to combine. Cook flour mixture 2 - 3 minutes.
Add seafood stock, wine, sherry (if using), paprika and bay leaves. Cover and turn heat down to medium low.
Simmer for 30 minutes, or until vegetables are completely soft. Remove bay leaves.
Carefully ladle soup into blender and purée until smooth. Add cream to blender and purée for a few seconds to blend in the cream.
Pour into bowls, top with langostinos and finely chopped chives. Serve immediately.