Heat your oven to 350°F. Grease a 9x9-inch baking dish and line it with parchment paper, leaving an overhang on two sides for lifting out the brownies later.
In a large bowl, vigorously whisk the eggs, yolk, and sugar for 2-3 minutes until thick and pale. Mix in the sourdough discard, oil, vanilla, and salt.
In a medium bowl, whisk together the cocoa powder, flour, and chocolate chips.
Add the dry ingredients to the wet ingredients and stir until combined.
Scrape the batter into the baking dish and smooth it out with a rubber spatula.
Bake for 35-40 minutes, or until a toothpick in the center comes out with a few crumbs.
Let the brownies cool in the pan for at least 30 minutes before cutting.
Nutrition information is calculated using an ingredient database and should be considered an estimate.