Hi, I moved back to Argentina after living for several years in Ireland and find it difficult to get some ingredients here. In particular cream of tartar and lemon curd - I am trying to find something similar and I just can't. Please help me out on this. I am dying to try your Lemon Meringue Cake (Feast, p170)! Thank you!
Cream of tartar is an acid and it is used in making meringues to help stabilize the egg whites meaning that they will whisk to greater volume and are less likely to weep (the acids help to denature, or unwind, the proteins in the whites making them easier to whisk). If making meringues you can use lemon juice or white wine vinegar instead if in small quantities. For the Lemon Meringue Cake we suggest using 1 teaspoon of lemon juice instead of the 1/2 teaspoon cream of tartar. If you are using cream of tartar and bicarbonate of soda (baking soda) in a baking recipe then you can replace BOTH of these with baking powder. Add the cream of tartar and bicarbonate of soda together and replace with baking powder with the same amount plus 1/3 extra (ie 1 teaspoon baking powder for every 3/4 teaspoon bicarb/cream of tartar).
Unfortunately there is no real substitute for lemon curd but it is relatively easy to make your own as it only uses eggs, lemon juice and zest, sugar and butter - Nigella has a recipe in How To Eat (p35) or you should be able to find recipes on-line. The cake needs 150g (2/3 cup) curd which mens you are likely to have some left over but lemon curd will keep in the refrigerator for a week and is delicious spread on toast or bread or spooned into small pastry cases to make mini lemon tarts.