I prefer to use lower fat buttery spreads such as Lurpak lighter in baking. Will this work in the Chocolate Chestnut Refrigerator Cake, or would it prevent the cake from setting?
Buttery spreads contain butter and milk solids, but also water, vegetable oils and stabilizers. The combination of vegetable oils and stabilizers help the spread to be soft and spreadable directly from the fridge. We do not generally recommend using these spreads in baking as they can affect the texture and keeping qualities of the finished cakes and cookies.
However the Chocolate Chestnut Refrigerator Cake (from Nigella Bites and on the Nigella website) is not baked but chilled to set the mixture. As the proportion of butter is low relative to the other ingredients, and as chocolate tends to set mixtures fairly firmly when chilled, we suspect that in this specific case a buttery spread could be used. But we have not tried it in this recipe so we cannot guarantee the results. However do be aware that the cake made with a soft spread may become difficult to slice if the cake is left out of the fridge for too long. Only remove the cake from the fridge just before serving and use a heavy, sharp knife to cut the cake. It may help also to dip the knife in a jug of very hot water before each slice.