Preheat the oven to 350°F (175°C) and either grease an 8x8-inch baking pan or line it with parchment paper.
In a small saucepan over low heat, melt the butter and chopped chocolate, stirring occasionally until smooth.
Remove it from the heat and let it cool for a bit.
In a mixing bowl, whisk together the brown sugar, eggs, vanilla extract, and sourdough discard until smooth and well combined.
Pour in the cooled butter-chocolate mixture and whisk until glossy.
In a separate bowl, sift together the flour, cocoa powder, baking powder, salt, and optional espresso powder or cinnamon.
Gently fold the dry ingredients into the wet mixture until just combined, taking care not to overmix.
Mix in the chocolate chips, making sure they are evenly spread throughout the batter.
Spread the batter evenly in the prepared pan. Bake for 25 minutes, or until the edges are set and a toothpick inserted in the center comes out with a few moist crumbs.
Let the brownies cool in the pan for about 10 minutes, then transfer them to a wire rack to cool fully before slicing and serving. Enjoy!