Preheat the oven to 350 degrees Fahrenheit. Line a baking pan with parchment paper and set aside
Add the 8 ounces of chocolate (please note this is 8 ounces by weight, not volume! see notes if you don't have a kitchen scale) to a bowl and melt in 30 second intervals in the microwave, stirring between each interval until fully melted. Alternatively, add to a double boiler and melt on the stove.
Melt the coconut oil and measure out ⅓ cup. Set the chocolate and oil aside for now.
In a mixing bowl or bowl of a stand mixer, beat together the eggs and sugar for about 2 minutes with an electric mixer. The long mixing time is key for the shiny crackly tops! After 2 minutes, beat in the coconut oil, melted chocolate and vanilla.
Beat in the cocoa powder, corn starch, flour, baking powder and salt. Be sure to spoon and level the flour. If you're using the espresso powder, also add this in now. I usually don't use it, but if you want a really rich chocolate flavor, it will do just that! The batter will be like a thick brownie batter, but not thick like traditional cookie dough. This is what you want!
Fold in the chocolate chips. Spray a medium cookie scoop with oil (this will help with the scooping since the dough is a bit sticky) and quickly scoop the dough and add to the prepared baking sheet, leaving a bit of space in between for spreading. Add a few extra chocolate chips on top if desired. The sooner you can get the cookies in the oven, the better. If the batter sits for too long, the cookies won't get shiny/crackly.
Bake for 11-14 minutes, I usually do 12 in my oven. They will continue to firm up as they cool so you want them slightly soft when they come out of the oven.
Use a round cookie cutter to swivel around the cookie to create a perfectly round shape.
Let cool on the baking tray, then sprinkle with sea salt flakes and enjoy! It's important to let them cool completely, otherwise the center of the bottoms can stick to the parchment a bit, so try to wait a good 20-30 minutes if you can!