Preheat and prep: Heat the oven to 350°F (175°C). Line an 8-inch square pan with parchment, leaving overhang to lift the brownies out. Lightly grease the parchment.

Melt butter and chocolate: In a heatproof bowl, melt the butter and chopped chocolate together. Use a microwave in short bursts or a bowl set over simmering water. Stir until smooth and glossy.

Whisk in cocoa and espresso powder: While the mixture is warm, whisk in the cocoa and espresso powder. This blooms the cocoa for a deeper, richer taste.

Add sugars: Whisk in the granulated and brown sugar until the mixture looks thick and shiny. It may appear grainy—that’s fine.

Beat in eggs and vanilla: Add the eggs one at a time, whisking well after each until fully incorporated. Whisk for about 30 seconds more to slightly aerate the batter, then stir in the vanilla.

Fold in dry ingredients: Sift or whisk together the flour and salt in a small bowl. Use a spatula to gently fold the dry ingredients into the batter just until no dry streaks remain. Do not overmix.

Add chocolate chips (optional): Fold in chips or chunks for extra fudginess. The batter will be thick and silky.

Spread and level: Scrape the batter into the prepared pan and smooth the top. Tap the pan once on the counter to release air bubbles.

Bake: Bake for 24–30 minutes, depending on your oven. The edges should be set, and a toothpick inserted 2 inches from the edge should come out with moist crumbs, not wet batter.

Cool completely: Let the brownies cool in the pan on a rack for at least 1 hour. For the cleanest slices and fudgiest texture, chill for 30–45 minutes before cutting.

Finish and serve: Lift out using the parchment, sprinkle with flaky salt if you like, and cut into 12–16 squares. Serve at room temperature or slightly chilled.