Combine flour, cocoa, coffee powder, salt, and baking soda in a bowl and set aside. 

In another bowl, mix together melted butter and sugars. Then stir in egg, egg yolk, and vanilla. Finally, add coffee liqueur and mix until well combined.

Gradually add flour to butter mixture until a dough forms. It may look too dry, but don't give up! Eventually it will come together. Finally, fold in chocolate chunks and chill dough in fridge for at least 30 minutes. 

Preheat oven to 325 degrees. Roll dough into golf ball sized balls. Bake on parchment paper (or a greased baking sheet) for 10-12 minutes, or until the edges are set and middles are still soft. The center should be slightly puffy. Do not overbake! Remove from oven, immediately sprinkle with salt, and then let cool completely.