Hello! When Nigella calls for "chiles" in recipes, is there a way to know if she means cayenne (long red hot peppers) or jalepenos (shorter often green hot peppers) or another type of pepper. I am from the U.S. and we have several types of hot peppers available in most grocery stores. Thanks!
Unfortunately the UK does not differentiate as much as the US between different chiles (UK spelling chillies). If the recipe states "chiles" it is most likely to be a jalapeno type chile with a medium heat. In the UK they are sold in both green and red form. The red jalepenos have been left to ripen longer and may be slightly sweeter than the green ones but the heat level is the same. In the US the vast majority of jalapenos are sold green and the ripened ones are more likely to be smoked to make chipotle peppers instead. Most of the time the fresh red chiles are used for purely aesthetic reasons (the flecks or red look attractive) and green jalepenos can be used instead. In the US Fresno peppers and Dutch peppers could also be used instead of jalapenos. Cayenne and Serrano peppers tend to be rather hotter so should only be used if you want extra heat.
Occasionally UK recipes will specify Bird's Eye chiles. These are very small but very hot chiles from Thailand and may also be sold in the US as Thai Chiles. They are less common in the US but can be found in Asian markets and some gourmet grocery stores. If you can't find Bird's Eye chiles than Serrano chiles are a good substitute, though bigger so you may need to use 1 Serrano per 2 Bird's Eye chiles.