• Preheat oven to 350°F. Grease and line a 9×5-inch loaf pan with parchment paper for easy removal.
• In a large bowl, whisk melted butter, sugar, and cocoa powder until smooth.
  
• Add eggs one at a time, whisking after each addition. Stir in vanilla.
• Gently fold in flour, baking powder, and salt until just combined — don’t overmix.

SWIRL

• Pour half the batter into the prepared loaf pan.
• Drizzle half the hot fudge over the batter and swirl lightly with a knife.
• Add the remaining batter, top with the remaining fudge, and swirl again for a marbled effect.
• Bake for 50–60 minutes, or until a toothpick inserted into the center comes out with moist crumbs (not wet batter). Let cool in pan for 15 minutes before transferring to a wire rack.