Nigella has listed sources for instant espresso powder for the UK and US. However I live in Sydney, Australia, and have not come across this in any shops locally. I can't really afford to buy much online as the delivery/postal charges tend to add to the cost quite a lot. Plus, even if I do buy on-line parcels frequently get lost. What do you suggest?
We are sorry that you are having difficulty sourcing the instant espresso powder. In Australia we understand that there is a coffee called Moccona Espresso Style instant coffee granules and we feel that this may be the best alternative. However as they are granules rather than powder, they need to be dissolved before use.
To use the same weight of granules as powder, you need to use 1 tablespoon plus 1/2 teaspoon of the espresso instant granules for each 1 tablespoon of powder (or 1 1/8 teaspoons granules per 1 teaspoon powder). You need to dissolve the granules in as little liquid as possible but we usually find that the same volume of just boiled water as coffee works well (1 tablespoon just boiled water for 1 tablespoon granules).
This should be a reasonable substitute for cakes and in Nigella's coffee ice cream. As the strength of coffees may vary between brands, you may find that you need to slightly adjust the quantities used to suit your own taste.
Regular instant coffee granules are weaker than the espresso type and so are not the best substitute. Some people also feel that the taste is harsher and less rounded than the espresso coffee. However if you need to use regular instant coffee then we suggest you try 1 1/2 times the quantity of the espresso powder (1 1/2 tablespoons instant coffee granules for each tablespoon espresso powder). Again the granules need to be dissolved in hot water, as outlined above and you may need to adjust quantities to suit your own taste.