Preheat oven to 350°F. Line a light-colored metal/aluminum 9×13-inch pan with parchment, leaving an overhang for easy removal.
In a large bowl, whisk together melted butter, sugar, and cocoa powder until smooth and glossy, ~2 minutes.
Whisk in eggs, egg yolk, vanilla, and salt until fully combined.
Fold in flour until just combined.
Stir in mini chocolate chips.
Spread batter evenly in the pan.
Bake for ~24-28 minutes, until the edges are set and the center is just set.
Let brownies cool completely in the pan. Then refrigerate for at least 2 hours (or freeze for 30-45 minutes) until firm.
Lift brownies out using parchment and place on a cutting board. Cut into even fry shapes about ¾ inch wide and 3-4 inches long.
Garnish with flaky sea salt or a dusting of powdered sugar if desired and serve with melted chocolate, chocolate ganache, caramel sauce, or a cold glass of milk.
