In the Pasta e Fagioli, is a "popsock" a muslin bag?
Nigella's Pasta e Fagioli (from NIGELLA BITES) is a robust and satisfying bean and pasta soup. The recipe cooks the beans from dried (rather than using canned beans) and the cooking liquid is infused with garlic, onion and rosemary. For ease the onion and rosemary are put into a popsock bag, so that you don't have to pick out pieces of onion and needles of rosemary once the beans have cooked.
Popsocks are knee-high nylon stockings. They are a useful size for using as a herb bag. Make sure that the popsock is clean and our preference would be to use an old, clean popsock rather than a new one straight out of its packaging. If you are using new popsocks then either first put them through a wash cycle or cover them with water from a freshly boiled kettle, add a couple of drops of washing up liquid (dishwashing liquid), let the water cool then remove the popsock and rinse thoroughly with fresh warm water before using. This should remove any dust or residue from the popsock. If you prefer to make a bag from muslin instead then this would also be absolutely fine.