I have tried making Nigella's Fudge recipe a number of times, and each time it's a disaster! The sugar doesn't dissolve and it is very grainy and crumbly. What am I doing wrong?
Nigella's Fudge (from Domestic Goddess) is a classic cooked fudge recipe using sugar, butter and evaporated milk. We suspect that the fudge is turning crumbly due to crystallization of the sugar in the mixture as the sugar has not dissolved properly when the mixture comes to a boil.
When making fudge you are controlling the formation of sugar crystals to get the correct texture. It sounds complicated but in practice it is fairly simple. Whenever boiling any sugar solution you should make sure that the sugar is fully dissolved before the mixture is brought to the boil, otherwise the undissolved sugar crystals will tend to cause the cooked mixture to become crusty and crystalline (the undissolved crystals attract the sugar molecules in the mixture and then form larger crystals).
Start the mixture in a saucepan over a low to medium heat and stir occasionally until you cannot see any undissolved sugar in the mixture, then raise the heat and bring to the boil. If possible also try not to stir the mixture when boiling, try swirling the pan gently instead if it looks like the mixture is cooking too quickly at the edges of the saucepan.
It could also be possible that the mixture is boiled for slightly too long. Fudge is made by boiling a sugar mixture to "soft ball" stage (115c/238F). If you are using a sugar thermometer then it may be worth checking the accuracy by putting the thermometer in a saucepan of boiling water (it should read 100c/212F).