The best way is to make homemade powdered sugar by grinding granulated sugar in a coffee/spice grinder or small high-speed blender and sifting it. Add 1 tbsp cornstarch (an anti-clumping ingredient) per cup of sugar if you plan to store it. Alternatively, add granulated sugar and lemon juice to a small saucepan to create a syrupy consistency rather than a regular glaze.