Set the butter, brown sugar and granulated sugar in a medium sized pot over medium low heat. Let the butter melt then whisk the mixture well. Continue to cook until it starts to bubble, then let it boil for another 1-2 minutes. Turn off the heat and add the cocoa (sift it in if it’s lumpy), whisk to combine.

Transfer the mixture to a medium to large sized bowl, add the vanilla and salt then give it a good whisk (you’ll see it start to clump into the whisk). Let cool for at least 5 minutes.

Add the egg yolks and quickly whisk well. Add the sourdough discard and whisk until you have a smooth, shiny batter. Add the flour, baking powder and baking soda and switch to a spatula to stir and combine.

Before adding the chocolate chips, check to ensure that the dough is cool (if you add them too soon, the chocolate will melt into the dough). Once cool, stir in the chips and cover the bowl with plastic wrap. Set in the fridge to chill for at least 3 hours, and up to overnight (about 8-10 hours).

Preheat the oven to 350 F. Grease then line two baking sheets with parchment paper. Scoop the cookie dough onto the prepared sheets in balls that are about 2 tablespoons each. Leave enough space for them to spread, an inch around.

Bake the cookies for 12 minutes, the centers should look matte and dry. Let cool briefly on the pan then transfer to a cooling rack.

Store leftovers in an airtight container.