Melt butter and chocolate in a bowl over simmering water then set aside
In another bowl beat together egg, granulated sugar, brown sugar and the sourdough discard
Pour the melted butter and chocolate mixture into the egg mixture and mix until well combined
Sift in flour, salt and cocoa powder and fold the mixture together
Divide the dough into 9 equal balls using either an ice cream scoop or spoon. Do not soften the surface, in fact try to keep it as rough as possible for a nice, crackly surface
Place them onto a large baking tray lined with parchment paper. Leave space in between them. Let them rest in the freezer for 10 minutes
Pre-heat oven to 180 C / 356 F
Remove the baking tray from the freezer and bake the cookies for 15 minutes
Notes
TIP: After 10-12 minutes remove the tray from the oven and tap it a few times onto the kitchen counter. This will help to achieve the brownie like crackly crust on the top of the cookies.