Heat the oven to 350°F (175°C). Line an 8-inch square metal baking pan with parchment paper, leaving enough paper over the sides to lift the cooled brownies out easily.

Whisk the melted butter, neutral oil, and granulated sugar together in a large bowl until well combined. Add the eggs and vanilla extract, then whisk until smooth and slightly lighter in texture.

In a separate bowl, sift or whisk together the all-purpose flour, unsweetened cocoa powder, and fine salt. This distributes the cocoa and salt evenly and helps prevent dry pockets in the finished batter.

Fold the dry mixture into the wet mixture just until no dry streaks remain. Avoid overmixing, because too much stirring can make brownies less tender.

Fold most of the semisweet chocolate chunks or chips into the batter, reserving some for the top. Spread the batter evenly into the prepared pan and sprinkle the reserved chocolate over the surface.

Bake for 20–25 minutes, until the edges look set while the center remains slightly soft and moist. A toothpick inserted into the center should come out with moist crumbs, not wet batter.

Cool the brownies in the pan for at least 30 minutes before cutting. For especially neat, dense squares, cool them fully and chill them briefly before slicing with a sharp knife.