For how long do you have to preheat oven for Christmas Cupcakes, Soft White Dinner Rolls, Dark and Sumptuous Chocolate Cake and Chocolate Mint Cookies?
Also do I use heaped or level teaspoons of baking powder when adding it to plain flour to turn it into self-raising flour? Does it matter?
All of Nigella's baking recipes, such as the Chistmas Cupcakes, Soft White Dinner Rolls, Dark and Sumptuous Chocolate Cake and Chocolate Mint Cookies give the recommended oven temperature and the oven should always be fully preheated before the prepared bread or cakes are put into the oven. However you need to start preheating the oven before you make the recipe as most items, particularly cakes, need to be baked as soon as they have been mixed. Unfortunately ovens vary and the time needed to preheat your oven will depend on the type and age of the oven, but most ovens have an indicator light to show that the oven has reached the set temperature. Usually if you switch on the oven before you start to weigh out cake or cookie/biscuit ingredients, then most ovens will be fully heated by the time you have mixed the batter or dough. But if you have an older oven you may need to allow a little longer. If you are making yeasted bread or rolls then we suggest switching on the oven about 10 minutes before the dough has completed its second rise.
To convert plain (all-purpose) flour to self-raising flour, Nigella usually adds 2 teaspoons of baking powder to each 150g (1¼ cups) plain flour. In Nigella's recipes the teaspoon and tablespoon measures are always level unless otherwise stated. Also the teaspoons used are from a standard measuring set of spoons (one teaspoon is 5ml). For leavening such as baking powder or bicarbonate of soda (baking soda) it is very important to use the level measures, as too much leavening will affect the finished recipe and a small difference can have a big effect.