Preheat oven to 350°F. Line a baking sheet with parchment paper. Set aside.
In a medium-sized bowl, whisk together flour, cocoa powder, baking soda, baking powder, salt, and espresso powder. Set aside.
In a large bowl, add the butter, brown sugar, and sugar. Using a stand mixer or hand mixer, beat until light and creamy, about 3 minutes.
Add egg yolks, and vanilla extract. Beat until well combined. Scraping down sides of bowl as needed.
Add dry ingredients and mix on low speed until combined. Scrape down sides of bowl.
Using a cookie scoop, scoop about 2-3 tablespoons of dough onto prepared baking sheet, about 3 inches apart. Bake for 12-15 minutes, until cookies spread out and the top begins to crack (be careful not to overbake the cookies, they should be soft when removed from oven). Transfer to a wire rack to cool completely.
Buttercream Icing
In a large bowl, add the butter, powdered sugar, heavy cream, vanilla and salt. Beat using an electric mixer until smooth, light, and fluffy. Add icing to a piping bag fitted with a large round tip.
Decorate
Pipe the icing onto the cooled cookie into a swirl. Top with crushed candy canes. Enjoy immediately or store in an airtight container until ready to serve.