Preheat the oven to 350 degrees F.
Line an 8-inch baking dish or cake pan with parchment paper. You can also grease the pan or spray it with nonstick spray, but I never do.
In a saucepan over low heat, melt together the butter sugar, and chocolate, stirring often. Continue to stir/whisk until the mixture is smooth and shiny. Be sure to keep a close eye on it to make sure the chocolate doesn't burn. Remove from the heat and set aside.
In a large bowl, combine the flour, salt, and cocoa powder.
Add the vanilla and sourdough discard to the chocolate mixture and whisk well. Then add the eggs one at a time, making sure that each egg is completely mixed in before adding the next one.
Finally, pour the chocolate mixture into the flour mixture and gently fold until combined. Your brownie batter should be wet and fairly thick.
Pour the finished batter into the prepared pan, be sure to scrape out as much batter as possible with a rubber spatula.
lace the pan in the oven. Bake for 20-25 minutes or until the brownies pass the toothpick test. (a toothpick inserted into the center of the pan comes out clean.)
Remove the pan from the oven and allow the brownies to cool completely before cutting. Cooled brownies can be topped with powdered sugar, and sea salt flakes, or served plain.