Preheat your oven to 350°F (175°C) and prepare an 8x8-inch baking pan by greasing or lining it with parchment paper.

In a medium bowl, combine the melted butter and granulated sugar. Mix until smooth, then add the eggs one at a time and vanilla extract, stirring until thick and creamy.

Sift in cocoa powder, flour, baking powder, and salt into the wet mixture. Fold until just combined, then add mini chocolate chips if desired.

Pour the brownie batter into the prepared pan and bake for 20-25 minutes until a toothpick comes out with a few moist crumbs.

Let the brownies cool in the pan for about 15-20 minutes before transferring to a wire rack to cool completely.

In a saucepan, combine heavy cream, butter, and vanilla extract over medium-low heat. Stir until melted, then add marshmallow fluff and stir until smooth.

Once cooled, pour the marshmallow topping over brownies and spread evenly, then sprinkle shredded coconut on top.

Refrigerate for at least 30 minutes to allow the marshmallow topping to set, then slice into squares.