Preheat your oven to 350°F (175°C). Line an 8 x 8-inch (20 x 20 cm) metal baking pan with parchment paper, leaving an overhang on two opposite sides. This makes it easier to lift the brownies out after cooling. Press the parchment into the corners so the batter can spread evenly.

Place the 1/2 cup (113 g) cubed unsalted butter and 4 ounces (113 g) chopped semisweet chocolate in a medium microwave-safe bowl. Microwave in 20-second intervals, stirring between each interval, until the mixture is nearly melted. Continue stirring until completely smooth. Alternatively, melt the ingredients in a heatproof bowl set over a saucepan of gently simmering water, making sure the bowl does not touch the water. The finished mixture should be smooth, glossy, and fluid, without visible lumps. Allow it to cool for approximately 3–5 minutes while preparing the remaining ingredients. It should feel warm rather than hot.

In a large mixing bowl, combine: 3/4 cup (150 g) granulated sugar 1/2 cup packed (100 g) light brown sugar 2 large eggs (about 100 g without shells) Whisk vigorously by hand for approximately 2–3 minutes, until the mixture looks slightly lighter, thicker, and glossy. The sugar may not dissolve completely, but the mixture should be well combined. This step helps encourage the characteristic thin, crackly brownie top.

Slowly pour the warm melted chocolate mixture into the egg and sugar mixture, whisking continuously. Add 2 teaspoons (10 ml) vanilla extract and mix until evenly incorporated. The batter should now look dark, glossy, and relatively thick but still pourable. If the chocolate mixture has cooled enough to become stiff, gently warm it before combining. Avoid adding very hot chocolate directly to the eggs.

Sift the following ingredients directly over the chocolate mixture: 1/2 cup (60 g) all-purpose flour 1/3 cup (28 g) unsweetened natural cocoa powder 1/2 teaspoon (3 g) fine salt Use a silicone spatula to gently fold the dry ingredients into the batter. Stop mixing as soon as no visible streaks of flour remain. The batter should be thick, smooth, and glossy. Overmixing after adding the flour can develop gluten and make the brownies tougher.

If using, add 1/2 cup (85 g) semisweet chocolate chips. Gently fold them into the batter until evenly distributed. The chocolate chips create small pockets of melted chocolate throughout the brownies, making the centers even richer. The batter should remain thick enough to hold soft folds when stirred.

Scrape the brownie batter into the prepared 8-inch square pan. Spread it evenly into the corners using a silicone spatula. Smooth the surface lightly, without pressing down excessively. The batter should form an even layer so the brownies bake at approximately the same rate from edge to center.

Place the pan on the center oven rack: Bake at 350°F (175°C) for approximately 27–33 minutes, using 30 minutes as a starting point. Look for these signs of doneness: The edges appear set and slightly firm. The top has developed a thin, delicate crust. The center no longer looks wet or liquid. A toothpick inserted near the center comes out with moist, sticky crumbs rather than loose, raw batter. Avoid waiting for a completely clean toothpick. That usually means the brownies have baked beyond the ideal fudgy stage. If the center still looks liquid, bake for another 2–3 minutes and check again.

Remove the pan from the oven and place it on a wire rack. Let the brownies cool in the pan for approximately 1 hour 30 minutes, or until completely cooled and sufficiently firm to slice. The center will continue to set as the brownies cool. Cutting while they are still hot can cause the soft chocolate interior to smear or fall apart.

Use the parchment overhang to lift the cooled brownies from the pan. Place them on a cutting board and use a sharp knife to cut them into 16 equal squares. For cleaner edges, wipe the knife between cuts. The finished brownies should have a delicate crust, firm edges, and a moist, dense chocolate center. Serve at room temperature for a soft, fudgy texture.