Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.
In a large bowl, whisk together the melted butter and granulated sugar until combined.
Add cocoa powder, salt, and baking powder. Whisk until fully incorporated.
Beat in the eggs one at a time, then stir in the vanilla extract.
Gradually mix in the flour until just combined. Do not overmix.
Spread the batter evenly into the prepared baking pan.
Bake for 25-30 minutes, or until a toothpick inserted into the center comes out with moist crumbs.
While the brownies are baking, prepare the ganache. Place chopped chocolate in a heatproof bowl.
Heat the heavy cream and butter in a small saucepan over medium heat until simmering. Do not boil.
Pour the hot cream mixture over the chocolate. Let it sit for 5 minutes, then whisk until smooth and glossy.
Once the brownies are out of the oven, let them cool slightly in the pan before pouring the warm ganache over the top.
Spread the ganache evenly. Let the brownies cool completely before cutting.
Notes
For an extra rich flavor, use dark chocolate chips in the brownie batter. Store leftovers in an airtight container at room temperature for up to 3 days.