Preheat oven to 350 degrees F. Lightly grease a 8x8 baking pan with butter and line with parchment paper on all sides. Make sure to leave some overhang on all 4 sides.
In a bowl set on top of a pot with simmering water (bowl should not touch water), melt the butter and chopped chocolate bar. Using a rubber spatula, stir until the mixture is melted and smooth. Turn off the heat. Set bowl aside and gradually whisk in the sugar until nicely melted.
Transfer mixture to another bowl since the one you’re using is a bit hot and we don’t want that when mixing the remaining ingredients. Whisk in eggs, one at a time, making sure it is nicely combined before adding the next one. Whisk in the vanilla extract. Mix in the cocoa and salt until the batter is smooth.
Fold in the flour, scraping the sides, until fully combined. Then, fold in chocolate chips.
Pour the batter into the prepared pan and gently smooth out the surface.
Bake for about 38-40 minutes, until set and a cake tester or toothpick inserted into the center comes out clean (a few moist crumbs in the tester is fine). Lift brownies from pan. Remove the parchment paper and let cool on a wire rack.
Cut into squares and enjoy!