In the bowl of an electric mixer using the paddle attachment, blend the egg whites and sugar together on medium speed until just foamy.
On low speed, add flour and melted butter.
Remove 2 tablespoons of batter to a small bowl and mix in cocoa powder. Place this cocoa batter into a pastry bag fitted with a small plain tip. Put aside.
On a parchment-lined or silicone mat-lined sheet pan place a teaspoonful of batter.
Using a small spoon or offset spatula, spread the batter into a three-inch circle.
Repeat the above procedure with more batter leaving a space around each circle.
When the sheet pan is covered with circles of batter, using the cocoa batter, pipe tiny dots randomly over each circle of batter. Bake them for 6-9 minutes, rotating the sheet pan midway, until the cookies are light brown around the edges.
After baking, roll each cookie around the handle of a greased wooden spoon to make a pirouette. As the cookie cools gently slide it off the handle and place it onto a plate. Repeat with the remaining cookies.
If the cookies cool and become hard before you can roll them, return the sheet pan to the oven to soften them for a few seconds.
Repeat the above procedure making pirouettes, until all of the batter is used up.