Melt the butter and chocolate: Melt the butter in a small saucepan. Place chopped dark chocolate in a large mixing bowl. Pour hot butter and espresso (or strong brewed coffee) over the chocolate, stir using a spatula until completely melted. Set aside and let the mixture cool for 5 minutes.

Whisk in sugars: Whisk the brown sugar and granulated sugar into the cooled chocolate and butter until the sugars are dissolved and the mixture looks smooth and thickened.

Make the dough: Add the sourdough discard, egg, vanilla, all-purpose flour, baking powder, salt and cocoa powder in that order into the mixing bowl. Stir until no traces of discard or egg and no dry bits of flour remain.

Stir in chocolate chips: Stir the chocolate chips in until they are evenly distributed throughout the dough. Cover the bowl with plastic wrap and refrigerate the dough for 15 minutes to allow the dough to firm up and become a little less sticky.

Prep: While your dough is chilling, preheat the oven to 375 F and line two large baking sheets with parchment paper.

Portion out cookie dough: Take the cookie dough out of the refrigerator and portion them out using a large cookie scoop (3 tablespoon or 50 gram portions). Roll the dough out into rounds and flatten the top lightly. Arrange the cookie dough on your prepared baking sheets at least 2 inches apart.

Bake: Bake the cookies for 8 to 10 minutes or until the cookies have flattened out, the tops look dry and the edges look set. Take the cookies out of the oven and let them cool completely on the baking sheets. Your cookies will not be completely set at this point, so do not move them.

Enjoy and store: These cookies are best enjoyed once they have completely cooled and set, they are even better the next day! Store any leftover cookies in an airtight container at room temperature for up to 7 days.