Heat butter in large pot over medium heat.
Add onion and celery, cook until soft.
Stir in tomato paste, cook for two minutes.
Pour in seafood stock and bring to boil.
Add shrimp, cook for three minutes until pink.
Remove shrimp, set aside to cool completely.
Add crab meat to the simmering stock.
Cook for five minutes, stirring very gently.
Blend soup until smooth using immersion blender.
Strain mixture through fine-mesh strainer twice.
Return to pot, add cream and sherry.
Season with salt and pepper to taste.
Add cooked shrimp back to the bisque.
Simmer for two minutes before serving hot.