Granulated Sugar (Best Option)
1 tablespoon per 1 tablespoon powdered sugarGranulated sugar works because it provides the same level of sweetness as powdered sugar without adding moisture. In a frittata, the heat and moisture from eggs and other ingredients help dissolve the sugar crystals, minimizing any graininess.
To ensure even sweetness, whisk the granulated sugar thoroughly with the eggs and other ingredients. Avoid adding it late in the cooking process to allow proper dissolution.
Compared to powdered sugar, granulated sugar may result in a slightly less smooth texture before cooking, but the final frittata will have a comparable sweetness and texture.