Preheat the oven to 350°F (175°C). Line an 8 x 8-inch (20 x 20 cm) metal baking pan with parchment paper, leaving some overhang on two opposite sides. This will make it easier to lift the brownies out after cooling.

Place 1/2 cup (113 g) unsalted butter in a large microwave-safe bowl. Heat in 20-second intervals, stirring between each, until completely melted. The butter should be liquid and warm, but not bubbling vigorously. Let it cool briefly if very hot.

Add 3/4 cup (150 g) granulated sugar and 1/4 cup packed (55 g) light brown sugar to the melted butter. Whisk vigorously for about 1 minute until the mixture looks thick, glossy, and evenly combined. It may still appear slightly grainy, which is normal.

Add 2 large eggs, one at a time, whisking thoroughly after each addition. Stir in 2 teaspoons (10 ml) vanilla extract. Continue whisking for 1 to 2 minutes until the mixture becomes smoother, thicker, and slightly lighter in color. This helps dissolve some of the sugar and encourages a delicate crust on top.

In a medium bowl, whisk together 1/2 cup (43 g) unsweetened cocoa powder, 3/4 cup (90 g) all-purpose flour, and 1/2 teaspoon (3 g) fine salt. Sift the mixture into the wet ingredients to break up any cocoa lumps.

Using a silicone spatula, gently fold the dry ingredients into the wet mixture until no visible flour streaks remain. The batter should be thick, smooth, and glossy rather than thin or runny. Stop mixing as soon as everything is incorporated to avoid developing too much gluten.

Fold in 1/2 cup (85 g) semisweet chocolate chips until evenly distributed. The batter should remain thick enough to hold soft folds when stirred. If it seems unusually stiff, check that the flour and cocoa were measured correctly before making adjustments.

Transfer the batter to the prepared pan and spread it evenly into the corners with a spatula. Smooth the surface gently so the brownies bake at a consistent thickness. Tap the pan lightly on the counter once or twice to settle the batter.

Place the pan on the center oven rack and bake at 350°F (175°C) for 25 to 30 minutes. The edges should look set and slightly pulled away from the pan, while the center should no longer appear liquid or wobble when gently moved. Insert a toothpick into the center, avoiding a chocolate chip. It should come out with a few moist crumbs, not wet batter. If needed, continue baking in 2-minute increments.

Remove the pan from the oven and place it on a wire cooling rack. Allow the brownies to cool in the pan for approximately 1 hour 30 minutes, or until completely cool. The center will continue to firm as it cools, making the brownies easier to slice without crumbling.

Use the parchment overhang to lift the cooled brownie slab from the pan. With a sharp knife, cut it into 16 equal squares, making four cuts across each direction to create a 4 x 4 grid of portions. Wipe the blade between cuts for cleaner edges. Serve at room temperature for a soft, fudgy texture.