If you can’t find fine granulated sugar, use food processor to grind regular granulated sugar to a fine powder. Or substitute granulated sugar.
When beating egg whites, to determine if sugar has dissolved, rub egg whites between your thumb and index finger; the mixture should not feel gritty.
If you don’t have a piping bag, cut a 1inch (1.5 cm) hole in the corner of a large Ziploc freezer bag, fill with cookie mix and gather at the top to form a piping bag. Cookies should be about 1 to 1-1/2 inches (2.5 to 4 cm) at the base.
Avoid making meringue cookies on a really humid day or they will be very sticky.