Granulated Sugar (Best Option)
1:1 by volumeGranulated sugar works well because it provides the same level of sweetness as powdered sugar without adding moisture. In quiche, where sugar is typically used in small amounts to balance flavors, the slight graininess is negligible and often undetectable after baking.
To ensure even sweetness distribution, whisk the granulated sugar thoroughly with the eggs and dairy before baking. Avoid using coarse sugar to prevent any gritty texture.
The final quiche will have a similar sweetness and texture to the original recipe, with no significant impact on the custard's smoothness.