Fry the Langoustine shells in olive oil with tomato paste, fennel, cayenne pepper, onion dill, dill seeds for a few minutes until golden
Add garlic, half the butter, water, white wine and brandy and let simmer for 30 minutes (not more) stirring occasionally and spooning out any excess eggwhite-foam.
Strain to get rid of solids and return liquid to the saucepan. Bring to the boil and reduce to half
Add the cream and cook at a steady simmer for 5 minutes
Taste and adjust seasoning with salt and pepper. Add remaining butter and a few more drops of brandy.
Refrigerate for up to 5 days, or freeze for up to 3 months.