Does the squid you buy come cleaned? In the US there's a lot of prep to do to get them ready, removing the cartilage, skin, and insides, and washing.
Nigella's recipe for Salt And Pepper Squid (from NIGELLA BITES) uses frozen then thawed baby squid. This is convenient as you can buy the squid ready cleaned and freezing also helps to tenderise the flesh of the squid.
In the US if you look for packages labelled "tubes" these are usually cleaned squid, and may also include the tentacles. In the UK frozen packages can be bought in some major supermarkets (though may not be exactly the 500g size mentioned) and are usually cleaned. Alternatively you could buy from a fishmonger and ask them to clean the squid for you. It is also not that difficult to do at home. Start by thawing the squid overnight in the fridge then pull on the tentacles to remove the head and innards. Cut the tentacles off and remove the bony centre piece (called the "beak"). Discard the head, beak and innards. Pull out the clear cartilage from the body tube and then pull out the dark, spotty skin from the inside and discard both of these. Rinse the squid tube and tentacles with cold water, pat dry and then the squid is ready to use for the recipe.