My son is lactose intolerant and I was wondering if I could substitute either almond milk, coconut milk, soy milk or a lactose free milk for the whole milk in the recipe? Also is it best to use whole milk rather than a lower fat milk?
Nigella's Nursery Fish Pie (from Feast) is made up from smoked and unsmoked fish which is mixed with a white (bechamel) sauce and topped with mashed potatoes flavoured with cheddar cheese. If you need to avoid lactose then we would prefer to use a lactose free version of cow's milk as this is the closest substitute. Failing this then soy milk would be the next closest, though make sure it is not flavoured or sweetened. Almond and coconut milks tend to have their own subtle flavours which could clash with the fish and so we would avoid these if possible.
Whole (full fat) milk is also preferable as it gives some richness to the sauce, reduced fat (semi-skimmed) and non-fat (skimmed) milks tend to make the sauce a little watery.
We would also mention that the mashed potatoes contain butter and cheese. Some people with lactose intolerance can eat these products and some cannot, so please check and use appropriate alternatives if necessary.