Preheat oven to 350 degrees Fahrenheit and line a cookie sheet with parchment paper.

In a small bowl, mix cocoa, baking soda, flour and salt until well combined.

In a medium bowl, beat together butter, sugar, eggs and vanilla until fluffy.

Gradually add in your cocoa mixture and beat well.

Use a cookie scoop to scoop dough and place onto the parchment paper. Place about 2 inches apart.

Bake for 10-12 minutes.

If you are going to ice your cookies, allow them to cool completely.

To make the icing:

In a medium bowl, combine the egg whites and vanilla and beat until bubbly.

Add powdered sugar in gradually and mix until all of the sugar is incorporated.

Beat on high until mixture forms stiff, glossy peaks.

Transfer icing to a pastry bag and pipe onto cookies.