In a medium size mixing bowl, cream together the softened butter and sugars.
Stir in the vanilla extract and egg until combined.
In another mixing bowl, whisk together the flour, cocoa, espresso powder, baking powder, baking soda, and salt.
Mix the dry ingredients in with the wet ingredients and stir until a thick batter forms.
Stir in the chopped dark chocolate.
Spoon onto a baking sheet lined with a baking mat or parchment paper. Top with flaky sea salt if using.
Bake at 350°F for 8-9 minutes. Allow to cool on baking pan before moving to a cooling rack.
Optional: Drizzle melted chocolate over the tops of the cooled cookies and allow to set.
Notes
You can substitute instant coffee powder for espresso powder if you need to. But I do prefer espresso powder if possible. I like chopped dark chocolate, but you can substitute for chocolate chips if needed.