For Nigella's Pineapple Upside Down Cake, can I use salted butter if unsalted isn't available? Or vegetable oil and milk?
Nigella prefers to use unsalted butter for baking and cooking as it lets the cook control the salt content to their own taste. Historically unsalted butter was also used for baking as it was fresher, as salt was added to help lengthen the shelf life of butter, but with modern refrigeration this is no longer an issue. In the recipe for Pineapple Upside Down Cake (from NIGELLA EXPRESS) Nigella does not specify either salted or unsalted butter, though unsalted would be the preference.
However it would be possible to use salted butter if unsalted is not availalble and we would look for a butter that is "slightly salted" or "demi-sel", as this will have a slightly lower level of salt. As brands can vary you could also look in the nutritional information box, which will give the amount of salt per 100g, and choose one with the lowest salt content. We would not particularly recommend using a combination of oil and milk for the cake batter as it is likely to be a little too liquid and in our experience this type of sponge has a better flavour when made with butter.