What does Nigella you mean when she writes in a recipe "thick cream or double cream"? Thank you so much !
In the UK there are several types of cream. Single, whipping and double cream come in pourable form. Whipping and double cream can both be whipped. In the last decade a type of cream has also appeared in supermarkets which has been labelled as "extra thick cream" or "spooning cream".
This cream usually comes as "extra thick double cream" and has the same fat content as double cream. However after pasteurizing it is heated and then cooled quickly, which gives the cream a thicker consistency. It is not as thick as clotted cream which is made by heating and then slowly cooling the cream and skimming off the thickened "clots" for cream. Clotted cream has a much higer fat content than double and extra thick cream.
Extra thick cream is usually served spooned over desserts. It can also be used for cooking but it is not suitable for whipping.