Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking pan or line it with parchment paper for easy removal.
In a large mixing bowl, combine the melted butter and granulated sugar. Stir until well combined.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, salt, and baking powder. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Pour the brownie batter into the prepared baking pan and spread it evenly. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Allow the brownies to cool completely in the pan on a wire rack. Once cooled, remove from the pan and cut into squares.
Take one brownie square, add a scoop of softened ice cream on top, and then place another brownie square on top to create a sandwich. Repeat with the remaining brownies and ice cream.
If desired, drizzle with chocolate syrup and sprinkle with toppings. Serve immediately or freeze for 30 minutes to firm up before serving.