Prepare the Brown Butter and Chocolate: In a small saucepan, melt the butter over medium heat until it turns golden brown and has a nutty aroma. Be careful not to burn it. Remove from heat, add the dark chocolate, and stir until smooth. Set aside to cool slightly.

Whisk Eggs and Sugar: In a separate mixing bowl, whisk the eggs and both sugars together until the mixture becomes thick and creamy.

Combine Wet Ingredients: Pour the chocolate and brown butter mixture into the egg and sugar mixture, stirring gently to combine.

Add Dry Ingredients, Vanilla, and Sourdough: Add the cocoa powder, salt, vanilla extract, and sourdough discard to the bowl. Fold gently until just combined, being careful not to overmix.

Prepare for Baking: Preheat the oven to 180°C (350°F). Line an 8-inch (20 cm) square baking pan with parchment paper, then pour the brownie batter into the pan and spread evenly.

Bake: Bake for 25-30 minutes, or until the brownies are set but still fudgy in the center. Sprinkle flaky salt on top.

Cool and Serve: Let the brownies cool completely in the pan. For best results, chill in the fridge before cutting into squares.