I used icing sugar instead of caster in the Brownies recipe as I couldn’t find caster in Singapore supermarkets. It’s made the brownies a little too sweet. It also took double the time to cook - actually even 45 mins later I reckon it still could have use a bit of time. Can I get a measurement for icing sugar if I can’t get caster and suggested cooking time? Despite the above, they are still some of the best brownies I’ve ever had. Thanks.
Nigella's recipe for Brownies (from HOW TO BE A DOMESTIC GOODESS) uses caster (superfine) sugar as this yields a squidgy brownie with a crisp crust. The texture and crust of baked goods will depend on the amount and type of sugars used. We are not sure if you used the metric weight or cup measure for the sugar, but metric weight should give the same level of sweetness and if you used cup measures then you would actually have less sugar overall if using icing (confectioners') sugar.
As icing sugar dissolves almost instantly, we wonder if this created a more liquid batter and maybe extended the baking time. You may also have ended up with a softer crust on the brownie. Icing sugar usually contains some anti-caking agent, such as cornflour (cornstarch), which may also have affected the brownie batter. Unfortunately, we would not recommend using icing sugar for this recipe. Some granulated sugars are quite fine (such as the sugars sold in the US and parts of Europe), so may be suitable for the brownies. You can also grind granulated sugar in a blender or food processor to make it finer, though do this in short bursts or pulses as it is easy to grind for too long and end up with powdered sugar.