Make the Brownie Batter: Combine melted butter, sugar, and vanilla in a bowl. Whisk in eggs until smooth. Stir in flour, cocoa, and salt until the batter is thick and well combined.
Bake the Brownies: Preheat the oven to 350°F. Line a 9x13 inch baking dish with parchment paper or tin foil. Spread the batter evenly in the pan. Bake for 24-30 minutes until set but still slightly gooey in the center. Cool completely.
Prepare the Sundae: Slice the cooled brownies into 12 pieces. Place one brownie on a plate, top with a scoop of ice cream, drizzle with chocolate sauce, and sprinkle with mini chocolate chips.
Serve Immediately: Add any additional toppings as desired and enjoy!