Sugar

Pliny called sugar “a kind of honey made with reeds,” thus describing it in terms of the sweetener he and his fellow Romans knew best. In baking, sugar is important far beyond its ability just to sweeten. By interfering with the production of gluten, it tends to tenderize cakes and make them rise somewhat higher. In yeast goods, it provides food for yeast. It helps give many cakes a beautiful brown colour by caramelizing. Sugar also contributes to the fine texture of cakes, especially those using many eggs.

Cane and beet sugars are both sucrose, and for baking I have noticed no superiority of the former. It is important, however, that sugar dissolve easily when creamed with butter and that it melt during baking, so one must use fine or very fine granulated sugar. Lumps formed during storage can usually be broken apart. If that does not work, try sifting them or forcing them through a colander.

Confectioners (or powdered) sugar has starch added to it to prevent the formation of lumps. Aside from its uses in frostings, it is excellent simply dusted (through a sieve) over a cake before it is served.