Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius) and line an 8x8 inch baking pan with parchment paper.

Whisk together melted butter and granulated sugar in a medium bowl, then incorporate eggs and vanilla extract.

Sift together cocoa powder, flour, salt, and baking powder; fold into the wet ingredients until just combined.

Transfer batter to the prepared pan and bake for 22 to 25 minutes or until a toothpick comes out with few moist crumbs.

Cool the brownie slab completely in the pan, then transfer to a cutting board and trim edges before cutting into 1.25-inch squares.

Heat heavy cream until simmering and pour over the chopped semi-sweet chocolate; let sit for 5 minutes then stir until a smooth ganache forms.

Place brownie squares on a wire cooling rack over a parchment-lined tray and spoon ganache over each piece to coat the top and sides.

Allow the ganache to set for at least 1 hour at room temperature, then pipe decorative patterns using melted white chocolate.