Prepare the pan. Heat the oven to 350°F (175°C). Line an 8-inch square pan with parchment, leaving an overhang for easy lifting. Lightly grease the parchment.

Melt butter and chocolate. In a heatproof bowl set over a pot of barely simmering water, melt the butter and chopped chocolate. Stir until smooth, then remove from heat. Let it cool for 3–5 minutes so it’s warm, not hot.

Whisk in sugars. Add granulated and brown sugar to the warm chocolate mixture. Whisk until glossy and thick. This helps create that shiny top.

Add eggs and vanilla. Whisk in the eggs one at a time, beating well after each. Stir in the vanilla. Mix for about 30–45 seconds until the batter looks shiny and slightly thickened.

Combine dry ingredients. In a separate bowl, whisk flour, cocoa powder, fine sea salt, and espresso powder. This prevents clumps and keeps the batter smooth.

Fold it together. Use a spatula to gently fold the dry ingredients into the wet mixture. Stop as soon as you no longer see dry streaks. Overmixing makes brownies cakey.

Add mix-ins. Fold in chocolate chips or chunks if using. Keep some aside to sprinkle on top for extra texture.

Spread and smooth. Scrape the batter into the prepared pan and smooth the top. If you like, add a pinch of flaky sea salt.

Bake. Bake for 22–28 minutes. Start checking at 22. A toothpick should come out with moist crumbs, not wet batter. The center should look set but still soft.

Cool before cutting. Let the pan cool on a rack for at least 1 hour. For clean slices, chill the pan for 30 minutes after it cools, then lift the slab and cut with a sharp knife, wiping between cuts.