Pre-heat oven to 350℉ and line your baking sheets with parchment paper.
In a large bowl, add your softened butter, brown sugar and first part of your sugar and mix until combined. (reserve rest of your sugar for rolling)
Add egg, egg yolk, vanilla extract and vanilla bean paste. Mix until well combined and light and fluffy.
Add flour, cornstarch, cocoa powder, salt and baking soda and fold until just combined.
Scoop out your cookie dough into 1 inch balls. Roll in sugar and then roll in powdered sugar. This helps give the crackling effect.
Bake in a 350° oven for 10-12 minutes. Remove from oven, let cool and enjoy!!
For a puffier cookie, add 1/4 cup more of flour or chill your dough before baking.
