Step 1

Preheat oven to 400 degree F. Cut 2 pieces of parchment paper and using a ruler draw 12, 2 1/2 inch lines spaced about 3 inches apart. Place the papers written side down onto 2 baking sheets and set aside.

Step 2

In the bowl of an electric mixer, beat butter, sugar, and confectioner’s sugar with the paddle attachment until light and fluffy, about 3-5 minutes. Add egg whites and vanilla and mix until combined. Mix in flour.

Step 3

Transfer the batter to a large piping bag fitted with a 1/2 inch round tip. Pipe the batter onto the lined baking sheets using the guides you marked earlier.

Step 4

Bake in preheated oven for 10 minutes. Remove from oven and let cool 5 minutes before transferring to a cooling rack. Repeat with remaining batter.

Step 5

To make the ganache, place chopped chocolate in a medium size bowl. Heat heavy cream in a saucepan until it begins to simmer (do not let it boil!). Pour over chocolate and let sit 2-3 minutes. Gently stir until combined and chocolate has completely melted. Allow to cool and thicken until spreadable consistency.

Step 6

To assemble the cookies, spread the ganache onto the flat side of one cookie and sandwich with the flat side of another cookie. Repeat with remaining cookies.