Preheat oven to 350°F (175°C) and arrange a rack to the center of the oven. Line a 9×9” square baking pan with parchment paper. Set aside.

Combine butter and chopped chocolate in a large microwave-safe mixing bowl and heat in the microwave in 25-second intervals, stirring well in between, until butter and chocolate are melted and mixture is smooth (alternatively you may melt on the stovetop over a double boiler).

Immediately add cocoa powder and stir well.

In a separate bowl, combine sugar and eggs. Use a whisk to beat vigorously for about 2-3 minutes (or use an electric mixer on high speed for 1 minute).

Add sourdough discard and vanilla extract and stir well.

Drizzle melted chocolate mixture into egg mixture and stir until well-combined.

Add flour and salt and stir until completely combined and batter is uniform.

Stir in chocolate chips, if using.

Spread evenly into prepared baking sheet and bake in center rack of oven for 30 minutes or until a toothpick inserted in the center comes out with moist fudgy crumbs (or clean).

Allow brownies to cool in pan before cutting and serving.