Granulated Sugar and Cornstarch Blend (Best Option)
1 cup granulated sugar + 1 tablespoon cornstarch = 1 cup powdered sugarPowdered sugar is essentially finely ground sugar with a small amount of anti-caking agent, usually cornstarch. By blending granulated sugar with cornstarch, you replicate the fine particle size and moisture-absorbing properties, ensuring even sweetness distribution and smooth batter texture.
To ensure success, pulse the mixture until very fine but avoid overheating the blender which can cause melting. Sift the resulting powder before adding to the batter to remove any larger particles.
Compared to original powdered sugar, this substitute maintains the lightness and smoothness in the brownie batter, preserving the intended fudgy yet tender crumb without adding extra moisture or graininess.