Make Brownies Recipe with a glossy, fudgy center and crackly top; bake, cool, and serve warm for best results.
Preheat the oven to 350°F (175°C) and position the rack in the middle. Lightly grease an 8-inch (20 cm) square metal baking pan with the softened teaspoon of unsalted butter (or a quick spray), then line the bottom and two opposite sides with a single strip of parchment paper leaving a generous sling for lifting; lightly grease the parchment as well. This ensures easy unmolding and tidy edges once the brownies are baked.
Place the chopped semisweet chocolate and the 10 tablespoons of butter in a medium heatproof bowl and melt gently until smooth, either over barely simmering water or in short microwave bursts, stirring frequently. Remove from heat while warm and whisk in the granulated and light brown sugars until the mixture becomes thick, glossy and homogenous—warm, fluid, and deeply chocolate in color but not hot to the touch.

Let the chocolate mixture cool just until warm; then add the room‑temperature eggs one at a time, whisking vigorously after each until fully incorporated so the batter becomes noticeably thicker, shinier, and slightly lighter in hue. Whisk in the vanilla and fine salt until even—this stage produces the signature glossy, elastic batter that foreshadows a crackly top.

Whisk the all‑purpose flour and unsweetened cocoa together in a small bowl until evenly combined and lump‑free, then gently fold the dry mix into the chocolate batter with a silicone spatula using 20–30 strokes just until no dry streaks remain. If using, fold in semisweet chocolate chips or chunks and the toasted chopped walnuts or pecans with a few gentle strokes so they’re evenly distributed without overworking the batter.

Pour the dense, glossy batter into the prepared parchment‑lined square pan and use a spatula to push into the corners and smooth the top into an even layer. Bake 22–28 minutes, rotating once halfway, until the edges are set and the top is shiny and crinkled; for fudgier brownies aim for the shorter time. Remove from the oven and, if desired, immediately scatter the flaky sea salt over the hot surface. Let the pan cool on a wire rack for at least 30–45 minutes to set the crumb.

Use the parchment sling to lift the brownie slab from the pan onto a cutting board and trim into neat square pieces (9 large or 12–16 smaller). For the cleanest slices wipe a long sharp knife with a warm damp cloth between cuts. Serve squares slightly warm or at room temperature—on their own, or accompanied by a small scoop of vanilla ice cream, a dollop of whipped cream, or a drizzle of warm chocolate or caramel if you like.
