Line two-three baking sheets with parchment paper or a silicone mat. I have found tinfoil doesn't work well with these cookies - even when sprayed with cooking spray.
Dry Ingredients
In a medium Bowl, mix the flour, baking powder and salt if using. Either sift these ingredients or whisk vigourously to break up any lumps.
Eggs
In a medium bowl: mix the eggs, egg yolk, vanilla, and sugar together. It's easiest to use a hand mixer for this but you can use a whisk if that is all that you have. You want to mix until the ingredients are light in colour and foamy. This is what gives the cookies a crackle top.
Chocoalte
In a small-medium sauce pan: Melt the Chocolate and Butter on medium heat. Add in cocoa powder and coffee if using. Mix to combine.
Mix
Slowly pour the chocoalte sauce into the egg mixture and whisk while pouring it in. Stir to combine.Now add the flour mix. Stir until combine but do not over mix!
Bake
Using two spoons or a small cookie scoop add dallops of batter the prepared cookie sheets. Each cookie is 1.5 tablespoons worth of batter. I like to leave atleast 1.5" inbetween cookies as these cookies pread while baking.
Bake 10 minutes. Let the cookies chill on the cookie sheet.
Storage
Keep these cookie in an Airtight container or bag on the counter for 2 days. Any longer and you should keep them in the freezer.