Preheat your oven to 350°F (175°C) and grease a 9×5-inch loaf pan with butter or cooking spray.

In a medium bowl, whisk together the flour, cocoa powder, baking powder, and a pinch of salt until well combined.

In a large mixing bowl, blend the melted butter and granulated sugar until smooth. Add in the eggs one at a time and mix well. Integrate the vanilla extract.

Gently fold the dry ingredients into the wet mixture until just combined, avoiding overmixing.

Pour half of the brownie batter into the loaf pan, drizzle half of the hot fudge sauce, then repeat with the remaining batter and fudge.

Using a knife or skewer, gently swirl the batter and fudge together to create ribbons.

Bake for 45-50 minutes, checking for doneness with a toothpick.

Let the bread cool in the pan for 10 minutes before transferring to a wire rack to cool completely.