Preparation: Preheat oven to 350°F (180°C). Line a 9x13 inch baking pan with parchment paper, leaving an overhang.
Melt Chocolate and Butter: In a heatproof bowl over simmering water, melt chocolate and butter until smooth. Let cool slightly.
Mix Batter: In a large bowl, whisk sugar and eggs for 3-5 minutes until pale and fluffy. Gradually add the melted chocolate mixture.
Combine Dry Ingredients: Sift flour, cocoa powder, and salt. Gently fold into the batter. Add any optional mix-ins.
Bake: Pour batter into the prepared pan and smooth the top. Sprinkle sea salt if desired. Bake for 25-30 minutes until a toothpick comes out with moist crumbs.
Cool and Serve: Let brownies cool for at least 1 hour. Lift out using the parchment paper and slice.
Notes
For a gluten-free version, use a 1:1 gluten-free flour blend.
Add swirls of caramel or peanut butter for extra decadence.