Preheat your oven to 350°F (175°C). Grease or line an 8x8-inch baking pan with parchment paper.

In a medium saucepan over low heat, melt the butter and semi-sweet chocolate chips together, stirring constantly. Once melted, whisk in the cocoa powder and vanilla extract until smooth.

In a separate bowl, whisk together the eggs, extra egg yolk, white sugar, and brown sugar until light and slightly fluffy.

Slowly pour the melted chocolate mixture into the egg mixture, stirring continuously to prevent the eggs from scrambling.

Stir in the sourdough discard until fully combined.

Gently fold in the flour and salt until just combined. Do not overmix, as this can make the brownies tough.

Pour the batter into the prepared baking pan and smooth the top. Bake for 25-30 minutes or until a toothpick inserted in the center comes out with a few moist crumbs.

Allow the brownies to cool in the pan before cutting and serving for the best texture.