In a saucepan or microwave, melt butter and chopped chocolate together until smooth. Let cool slightly.
Whisk in granulated and brown sugar until glossy. Add eggs one at a time, followed by vanilla.
In a separate bowl, sift flour, cocoa powder, and salt. Fold gently into the wet mixture until just combined. Do not overmix.
Preheat oven to 350°F (175°C). Line a 9x13-inch pan with parchment. Spread batter evenly.
Bake 28–32 minutes, until set on the edges but slightly soft in the center.
Allow brownies to cool completely. Melt chocolate chips and drizzle over the top using a spoon or piping bag.
Cut into squares and garnish with fresh mint leaves for a bakery-style finish.
