white sugar
Refers specifically to refined white sugar, as opposed to brown sugar or other sweeteners.
This recipe uses white sugar.
黒砂糖 is brown sugar, often less refined and with a stronger molasses flavor.
Compound of 白 (しろ, 'white') and 砂糖 (さとう, 'sugar'). The reading しろざとう reflects rendaku voicing of the second element.