Reducing the sugar in Yule Log

Our answer

Unfortunately substituting sugar with alternative sweeteners will work in some type of baking and not others and we would suggest that Nigella's Yule Log recipe (from Christmas) is not a particuarly good recipe for these substitutions. The main problem with trying to use them in the Yule Log is that the batter for the Yule Log is made from whisking egg whites with sugar into a meringue, egg yolks with sugar to make a mousse-type mixture and folding these together with cocoa powder. The cake does not contain any regular flour and so does not have any gluten to give the batter extra "structure". So in this particular recipe the sugar itself is quite important as it helps to provide some structure to the batter.

Stevia doesn't melt under heat in the way that sugar does so is not particularly useful for delicate cake batters, though it may work in some cookie recipes if you add extra liquid to compensate. Fruit sugars tend to be sweeter than regular sugar so you need to reduce the qunatities used by up to 1/3, but this reduction can affect the structure of this particular cake batter and you may find that the cake is quite flat and crumbly. Fruit sugars also tend to brown more quickly so you would need to reduce the oven temperature by around 25c/50F.