Line your pan with parchment paper
Beat egg whites withhand blender or stand blender until whites are foamy;
beat in white sugar and continue beating until egg whites are glossy, fluffy, and hold soft peaks.
Sift powder sugar and ground almonds in a separate bowl and quickly fold the almond mixture into the egg whites,
Spoon a small amount of batter into a plastic bag with a small corner cut off and pipe a test disk of batter, about 1 1/2 inches in diameter, onto prepared baking sheet. If the disk of batter holds a peak instead of flattening immediately, gently fold the batter a few more times and retest.
When batter is mixed enough to flatten immediately into an even disk, spoon into a pastry bag fitted with a plain round tip. Pipe the batter onto the baking sheet in rounds, leaving space between the disks.
Let the piped cookies stand out at room temperature until they form a hard skin on top, about 20 to 25minutes
Preheat oven to 285 degrees F (140 degrees C). Bake cookies until set but not browned,
when it done .let it cool competely
Then you can sandwitch with your frosting.