Instructions

1. Melt the butter in a stock pot, sweat the onions for a few minutes ( do not let them brown), add the celery, carrots and leeks and sweat for a few minutes. Dust with flour, stir to combine and absorb.
2. Add the tomato puree, herbs and fish stock. Stir to combine with spatula and scrape sides of the pot to incorporate all the bits. 
3. Add the shells and add more stock or water until the shells are just about submerged. Bring to a boil and boil for 5 minutes. Cover the pot with the lid and reduce the heat to simmering. Simmer for 1 hour to allow the moisture and steam to extract flavour from the shells.
4. Remove lid and bring to a boil for 20 minutes to recuse the moisture and concentrate the flavour.
5. Remove little by little the shells from the stock pot to a sieve and bowl. Press with the back of a spoon or ladle the shells to render their juices. Disregard the shells.
6. Return the liquid to the stock pot, bring to a boil and add the cognac to evaporate the alcohol. You can also flame it if you are brave. Boil for 5 minutes then reduce the heat.
7. Add the cream and taste. Season with salt and pigment d'espelette. Taste and adjust seasoning if needed and serve.