1. Prepare the Crust:

1. Preheat oven to 350°F (175°C) and grease a 9×5-inch loaf pan.
2. In a medium bowl, whisk together flour, cocoa powder, baking powder, and salt.
3. In a separate bowl, mix melted butter and sugar until combined. Add eggs and vanilla, stirring until smooth.
4. Gradually fold the dry ingredients into the wet mixture until just combined.
5. Pour half the batter into the prepared loaf pan. Drizzle hot fudge sauce evenly over the batter, then top with remaining batter.
6. Bake for 30-35 minutes, or until a toothpick inserted comes out mostly clean (some fudge is okay).
7. Let cool in the pan for 10 minutes before transferring to a wire rack to cool completely.