Preheat your oven to 175°C. Grease and line an 8x8-inch baking pan with parchment paper, leaving some overhang for easy removal. In a microwave-safe bowl, melt 2/3 of the chocolate chips (about 67g) in 30-second intervals, stirring in between, until smooth. Set aside to cool slightly.
In a large mixing bowl, whisk together the melted butter and brown sugar until well combined. Add the egg and vanilla extract, whisking until smooth.
In a separate bowl, sift together the all-purpose flour, cocoa powder, and salt. Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Fold in the melted chocolate (2/3 portion) and remaining chocolate chips (1/3 portion).
Pour the batter into the prepared baking pan, spreading it evenly with a spatula. Bake in the preheated oven for 25-30 minutes, or until the top is set and a toothpick inserted into the center comes out with a few moist crumbs.
Remove the brownies from the oven and immediately sprinkle the remaining melted chocolate chips (1/3 portion) over the top. Allow the brownies to cool completely in the pan on a wire rack before slicing into squares.