What size is the cast iron skillet used for Eggs In Purgatory?
In Nigella's recipe for Eggs in Purgatory (from NIGELLISSIMA here and on Nigella.com here), the eggs are poached in a spicy tomato sauce in a small frying pan. Nigella usually makes this as a single portion in one of her "pixie pans", which is a cast iron skillet of around 16cm (6 1/2 inches) diameter. These pans are slightly difficult to find in the UK, though in the US Lodge make a pan of around this size. However any small frying pan would suffice.
A fairly common size for small frying pans is 20cm (8 inches) and this size is also fine for the recipe, particularly if you want to make it more substantial meal. With this slightly larger pan you can also cook 2 eggs, or drop one whole egg in and then drop in the yolk of a second egg onto the white of the first.