Melt the butter with the olive oil in a heavy pot over medium heat.
Cook the onion, celery, and carrot with a pinch of salt until soft and translucent, 7–8 minutes.
Stir in the garlic and tomato paste; cook until the paste deepens in color, about 2 minutes.
Sprinkle in the flour and cook, stirring, 1–2 minutes to remove the raw taste.
Deglaze with the sherry and simmer 1 minute to reduce slightly.
Pour in the seafood stock; add thyme, paprika, cayenne, black pepper, and remaining salt. Bring to a gentle simmer.
Simmer uncovered for 15 minutes to concentrate the flavors.
Blend the soup until perfectly smooth with an immersion blender; strain through a fine-mesh sieve if you want it extra silky.
Stir in the heavy cream, Worcestershire, and lemon juice; warm gently without boiling.
Fold in the crab, reserving a small handful for garnish; heat 2–3 minutes until warmed through.
Ladle into bowls, top with the reserved crab and herbs, and serve at once.