In a medium-sized saucepan, brown ½ cup butter over medium-low heat. Once butter is browned, remove the saucepan from heat and stir in 1 cup semi sweet chocolate chips until completely melted and smooth. Set aside on a wire cooling rack to cool for 10-15 minutes.
Preheat oven to 350f and prepare a 9x9 inch baking dish by lining with tin foil or parchment paper and spraying with cooking oil or greasing lightly.
Once the chocolate-butter mixture has cooled for 10 or so minutes, add 3 large eggs, ¾ cup granulated sugar, and ¾ cup brown sugar to the bowl of your stand mixer fitted with the whisk attachment. Beat the eggs and sugars at high speed for 2-3 minutes, until lightened in color and fluffy.
Add ½ cup of sourdough discard and beat again at high speed for 2 minutes, then without turning off the mixer, pour the chocolate mixture slowly down the side of the mixing bowl.
Combine 1 cup all purpose flour, ½ cup cocoa powder, and 1 teaspoon coarse kosher salt in a small bowl, and stir to combine.
Fold the flour mixture into the wet ingredients with a spatula. Stir only until completely mixed, avoid overmixing.
Pour the batter into the prepared baking dish.
Bake at 350f for 30-35 minutes, or until the edges look set and the center looks slightly undercooked.
Allow the sourdough brownies to cool to room temperature before cutting.
