Preheat oven to 350 ℉. Line 9x9 inch baking pan with parchment paper.
In a small bowl or glass measuring cup, melt butter and mix in cocoa powder to let it "bloom". Set aside.
¾ cup salted butter, melted, ¾ cup cocoa powder
In a mixing bowl, combine white sugar, eggs, sourdough discard, and vanilla and mix for 2-3 minutes until white and sugar is dissolving. You can whisk or use an electric mixer.
1 ½ cups white sugar, 2 eggs, ½ cup sourdough discard, unfed, 1½ teaspoons vanilla
Add in the butter/cocoa powder mixture and mix well.
Add in the flour and salt and mix well until all the flour pockets are gone.
½ cup all purpose flour, ¼ teaspoon salt
Fold in chocolate chips last.
½ cup semi-sweet chocolate chips, plus extra to sprinkle on top
Transfer to prepared 9x9 inch baking pan and bake for 35-40 minutes until inserted knife comes out clean. Let cool for 30 minutes before slicing for neater slices. Enjoy!