Caster Sugar with Cornstarch (Best Option)
1 cup caster sugar + 1 tablespoon cornstarch = 1 cup powdered sugarCaster sugar is finer than granulated sugar, allowing it to dissolve more readily in the mascarpone mixture. Adding cornstarch prevents clumping, mimicking the anti-caking effect of powdered sugar. This combination ensures the sweetener integrates smoothly without compromising texture.
For best results, pulse caster sugar and cornstarch in a food processor until very fine and well combined. Use immediately to avoid moisture absorption. Monitor the texture to ensure no graininess remains.
Compared to using pure powdered sugar, this substitute maintains the creamy and smooth mouthfeel critical to tiramisu, with negligible differences in sweetness or texture.