As shellfish are generally quite expensive, it makes sense to be using up every last part of the crustacean. The shells and legs (once meat has been extracted where possible) of lobsters, crabs, crayfish, langoustines and prawns impart a lot of rich flavour – especially after they're roasted. The heads also contain precious juices, and if you’re not keen on the idea of sucking on them at the dinner table, they should without a doubt be saved for stock.

To make shellfish stock, all you need is shells, vegetables, aromatics and water. How you prepare the shells will have an impact on the final flavour, so it's important to take a little time to roast them beforehand.

If you have some shellfish but don’t have time to make stock or want to save the shells up to make a bigger batch, you can break them down into smaller pieces and freeze until ready to use. You can also save the shells after they have been cooked and served – not every diner is meticulous when it comes to scraping out every last bit of meat, so you’re likely to be left with extra tasty morsels to flavour your stock with. Just make sure the shells are collected up and refrigerated or frozen straight after.

While some more old-school recipes require the whole crustacean including its meat, this is a touch extravagant and seems wasteful of the delicate and tender flesh of, say, lobster or langoustine. Carefully shell crustaceans and keep the meat separate from the shells to be cooked and eaten separately. Rinse any shells which may be hiding grit or sand (this is particularly important with crabs) and break down larger shells into smaller pieces. This gives them a larger surface area, which touches the bottom of the pan and caramelises, creating more flavour. The easiest way of doing this is by bashing the shells with a rolling pin in a deep pan or wrapped in a clean cloth.

Compared to fish stock, which has a light, almost perfumed flavour and should be clear in colour, shellfish stock has a rich, deep flavour and is red (due to the shells). As we are after a more robust flavour for shellfish stock, the shells are roasted first to help achieve a deeper flavour. Interestingly, the particles in crustacean shells are not only water soluble but fat soluble too, meaning frying the shells in a fat such as oil or butter before adding water is going to carry over from the pan to your finished stock.

When it comes to aromatics, herbs and spices, the same principle of enhancing that deep, caramelised flavour is applied. Sherry or more commonly brandy is added instead of (or as well as) white wine, which adds notes of caramel. As with a dark chicken or veal stock, tomato purée is added for a rich umami undertone and deeper colour. The usual onions, celery and garlic are used with the addition of carrots (which are omitted from fish stock) to boost that sweet flavour and again help achieve a nice deep orange-red colour. Vegetables are best sliced finely to produce more surface area to caramelise. Aniseed ingredients such as fennel and fennel seeds, dill, tarragon and chervil are all common additions which complement the fresh flavour of the sea. A sheet of kombu seaweed can also be added for a mineral-rich hit of umami.

As with all stocks, be careful with seasoning; this stock is cooked for two or three hours, over which time the flavour will intensify and potentially make it too salty. It is always best to leave salting until the end so you know you are happy with the final flavour.

The recipe below makes around a litre of incredibly flavourful stock. The shellfish shells can be made up of langoustines, prawns, crabs or lobsters, and can be precooked or, in the case of langoustines and prawns, peeled from the raw shellfish.

This highly aromatic stock can be reduced down a little and finished with a spoonful of cream or crème fraîche to create a simple yet stunning bisque. Adding the dairy gives it a velvety texture and mellows out the intensely sweet flavour. Other popular seafood dishes such as paella, risotto, gumbo or chowder are amplified ten times over by a top-quality shellfish stock. The classic French recipe for sauce Américaine follows a similar method to shellfish stock, but with the addition of fresh tomatoes and is flavoured with a dash of cayenne pepper. It is traditionally served with lobster.