Add all the finely chopped vegetables, excluding the garlic, to a large heavy-based pan along with the star anise, bay leaf, olive oil and butter. Sauté over a medium/low heat until soft but not coloured, around 10 minutes.
Add the garlic and sauté for 1 minute, add the tomato paste and paprika, and continue cooking for a further 5 minutes. Turn up the heat a little and add the white wine allowing it to bubble away for a couple of minutes.
Add the crab and stock and continue cooking for a further 10 minutes. Remove from the heat, discard the bay leaf and star anise, and blend until smooth with a stick blender.
Pass the soup through a sieve into a clean pan, add the cream and put back on the heat to warm through. Season with salt, pepper and lemon juice to taste.
Top the bread with the grated cheese and melt under a hot grill, ladle the soup into bowls and top with the cheesy croutons and reserved fennel fronds to serve.