Place the shells, bay leaves, fennel and lemon in a large pan
Cover with cold water and boil for 20 minutes before straining and reserving the liquid.
The bisque needs approximately 1.5 litres of stock so top up with boiling water, if needed.
Melt the butter in a large saucepan and cook the shallots, celery and carrot over a gentle heat until soft and fragrant.
Stir in the garlic and cook for a minute or two before adding the wine.
Cook until the wine is reduced by about half then stir in the cayenne and tomato purée, mixing well before sprinkling over the flour and whisking briskly to remove any lumps.
Cook for a minute or two then add the crayfish stock a little at a time, mixing well to ensure no lumps are forming.
Simmer gently until thickened, then blitz until smooth using a stick blender.
Pour through a sieve in a large bowl, pressing down with the back of a spoon to push through as much as possible.
Pour back into the pan and season to taste before reheating, adding the brandy and cream, if you fancy!
Ladle the soup into bowls and serve.