For the Milano Cookies:

1. Preheat the oven to 350 degrees F and line two baking sheets with parchment paper.
2. Create a template on one piece of parchment paper with 2 1/2" lines. You'll place this underneath the other pieces of parchment paper as a guide for piping the batter. 
3. Beat the butter and powdered sugar together for about 2 minutes until light and fluffy.
4. Add the vanilla and beat for one more minute.
5. Add the egg whites and beat for about 3 minutes until fully combined.
6. Mix in flour and salt until just combined. 
7. Transfer batter to a piping bag with a small round piping tip. (I used Ateco #803).
8. Pipe batter onto 2 1/2" lines on parchment paper and bake for about 10-12 minutes. 

For the Mint Chocolate Ganache:

1. In a small bowl, weigh out the chocolate. Set aside.
2. In a small saucepan, bring the heavy cream to just shy of a simmer. Pour over the chocolate and stir to combine.
3. If there are still pieces of chocolate, heat the ganache in the microwave in 10 second intervals until completely smooth.
4. Stir in peppermint extract, then place in the fridge for a few minutes until thick, but pipeable. 

For Assembly:

1. Transfer the ganache to a piping bag with a small round piping tip.
2. Pair the milano cookies up.
3. Pipe mint chocolate ganache on the bottom cookie and press the paired cookie on top.