Preheat your oven to 350℉. Butter your baking dish and set aside; my best results have been in an 8x8 or 9x9.
Melt your butter slowly and completely on the stove. Then add in your chocolate chips, cacao powder, and vanilla and combine JUST until melted. Remove from the stove and allow to cool down.
Beat your eggs and sugars in a mixing bowl. To this same bowl add your sourdough discard and melted chocolate mixture - mixing on low speed.
Fold in your flour and salt to the mixture.
Spread your batter in your prepared baking dish and bake for 25-35 minutes; until a toothpick comes out without batter on it.