I made Nigella's Old Fashioned Chocolate Cake but the icing turned out to be grainy because the sugar did not dissolve properly. So what should I do to rectify this mistake?
Nigella's Old Fashioned Chocolate Cake (from Feast) has an icing made from melted chocolate and butter that is then mixed with icing sugar, sour cream and golden syrup. The sugar used is icing sugar - sometimes known as confectioner's sugar or powdered sugar. This sugar is a very fine powder and should dissolve instantly.
We wonder if the sugar is not dissolving as another type of sugar is being used. If the icing sugar is switched for caster (superfine) or granulated sugar then the icing will be grainy as both of these types of sugar will not have the opportunity to dissolve. For most types of frosting and icing the very powdery icing sugar is used as it gives a very smooth finish.
If you can't find icing sugar then you can make a fairly close version of your own with a food processor or blender. Process 200g (1 cup) of granulated or caster sugar, using short pulses and stirring once or twice between pulses, until it becomes powdery. Use pulses as just running the motor can heat the blades of the processor or blender too much and cause some of the sugar to melt. Once the sugar has become powdery add 1 tablespoon of cornflour (cornstarch) and pulse to blend it with the sugar. This should yield 200g (scant 2 cups) icing sugar.