I want to make a traybake for 40 children for my son's 5th birthday. Can I use one of Nigella's chocolate cake recipes (I have all her books) and just quadruple the quantities and put it all in a big tray bake tin instead of my normal cake tin? Will that work? Will it still rise?
It can be quite difficult to convert chocolate layer cake recipes to traybakes (sheet pan cakes) as the baking time can vary so much and the cakes for a single layer cake generally need to be thicker than for a sandwich or two layer cake. However we suspect that Nigella's Dark And Sumptuous Chocolate Cake would convert to a 23x33cm/9x13-inch rectangular pan. The baking time could vary but start checking after 25 minutes and let the cake bake until it is done according to the recommendation in the recipe. However as we have not tried the cake in exactly this size we cannot guarantee the results. Make sure that you line the pan with baking parchment (parchment paper), with paper coming up the sides of the pan. A cake of this size will make approximately 16 portions and we would suggest making maybe two or three cakes rather than one very large one as very large cakes can be difficult to bake through evenly in a domestic oven. You can place the cakes together on a large tray or cake board and then stick them together with a little of the frosting, before spreading the remaining frosting over the top.
As an alternative you may want to consider Nigella's Brownies as these look very celebratory piled up and studded with candles. The recipe makes 48 bite-sized brownies or 18-24 larger brownies. Rice Krispie treats are also very popular with children and are a useful no-bake option. Nigella's Chocolate Rice Krispie Squares are a chocolate version that makes between 16 and 24 pieces. You can scatter the top with sprinkles or Smarties/M&Ms for a colourful finish.