For the Mock Mash, does it need to be full-fat milk or can semi- or skimmed milk be substituted?
Nigella's Mock Mash (from NIGELLISSIMA) is made from semolina (finely ground durum wheat) and the method is similar to making polenta. However, to get the creamy flavour and "mouthfeel" of mashed potatoes, the semolina is cooked with full-fat (whole) milk, and this would be our preference.
The Mock Mash could be made with semi-skimmed (reduced fat) milk, but you will need to add some extra butter, so that the dish retains its rich, creamy flavour. We would suggest adding one extra tablespoon (approx. 15g) of butter (so a total of 2 tablespoons/approx. 30g). Once you have added the cheese at the end of the recipe, taste the mixture and stir in a little extra butter if you feel that it needs it. We would prefer not to use skimmed (non-fat) milk as we suspect that the mash will end up tasting a little too thin.